DIRIGIBLE 

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DIRIGIBLE  BALLOONS 


INSTRUCTION  PAPER 


PREPARED  BY 

CHARLES  B.  HAYWARD 

MEMBER,  SOCIETY  OF  AUTOMOBILE  ENGINEERS;  MEMBER,  THE  AERONAUTICAL  SOCIETY; 
FORMERLY  SECRETARY,  SOCIETY  OF  AUTOMOBILE  ENGINEERS;  FORMERLY 
ENGINEERING  EDITOR,  “THE  AUTOMOBILE” 


AMERICAN  SCHOOL  OF  CORRESPONDENCE 

U.S.A. 


CHICAGO 


ILLINOIS 


COPYRIGHT,  1912,  1918,  BY 

AMERICAN  SCHOOL  OF  CORRESPONDENCE 


COPYRIGHTED  IN  GREAT  BRITAIN 
ALL  RIGHTS  RESERVED 


Lll  , 33J.  ' 

f)  sis.  D 

DIRIGIBLE  BALLOONS 

INTRODUCTION 

Of  the  first  attempts  of  men  to  emulate  the  flight  of  birds,  we 
have  no  knowledge,  but  one  of  the  earliest,  perhaps,  is  embodied 
in  the  myth  of  Icarus  and  Daedalus.  Xerxes,  it  is  said,  possessed 
a throne  which  was  drawn  through  the  air  by  eagles.  The  Chinese 
have  sometimes  been  given  credit  for  the  invention  of  the  balloon, 
as  they  have  for  many  other  scien- 
tific discoveries.  It  is  related  that 
- a balloon  was  sent  up  at  Pekin  in 
celebration  of  the  ascension  of  the 
throne  by  an  emperor  in  the  be- 
ginning of  the  fourteenth  century. 

Early  Attempts.  Leonardo  da 
Vinci  devoted  some  time  to  the 
problem  of  artificial  flight.  His 
sketches  show  the  details  of  bat- 
like wings  which  were  to  spread 
out  on  the  downward  stroke  and 
fold  up  with  the  upward  stroke. 

Francisco  de  Lana  planned  to  make 
a flying  ship  the  appearance  of  which 
was  somewhat  like  that  shown  in 
Fig.  1,  by  exhausting  the  air  from 
metal  spheres  fastened  to  a boat, 
with  oars  and  sails  for  propulsion  and  guiding.  The  method  in  which 
he  purposed  to  create  the  vacuum  in  the  spheres  consisted  of  filling 
them  with  water,  thus  driving  out  the  air,  then  letting  the  water  run 
out.  He  thought  that  if  he  closed  the  tap  at  the  proper  time,  there 
would  be  neither  air  nor  water  in  the  spheres.  His  flying  ship  was 
never  constructed,  for  he  piously  decided  that  God  would  never 
permit  such  a change  in  the  affairs  of  men. 


The  boat  was  to  be  equipped 


2 


DIRIGIBLE  BALLOONS 


The  First  Flying  Machine.  In  1781,  Meerwein  of  Baden, 
Germany,  constructed  a flying  machine,  and  was  the  first,  perhaps, 
to  intelligently  take  into  account  the  resistance  of  the  air.  He  took 
the  wild  duck  as  a basis  of  calculation,  and  found  that  a man  and 
machine  weighing  together  200  pounds  would  require  a wing  surface 
of  from  125  to  130  square  feet.  It  is  of  interest  to  note  that  Lilienthal, 
who  met  his  death  in  trying  to  apply  these  principles,  over  one  hun- 
dred years  later  found  these  figures  to  be  correct.  Two  views  of 
Meerwein’s  apparatus  are  shown  in  Fig.  2.  The  construction  involved 
two  wood  frames  covered  with  cloth.  The  machine  weighed  56 
pounds  and  had  a surface  area  of  111  square  feet.  The  operator 
was  fastened  in  the  middle  of  the  under  side  of  the  wings,  and  over 


Fig.  2.  Meerwein  Flying  Machine 


a rod  by  which  he  worked  the  wings.  His  attempts  at  flight  were 
not  successful,  as  his  ideas  of  the  power  of  a man  were  in  error. 

Classification.  All  attempts  at  human  flight  have  gone  to 
show  that  there  are  four  possible  ways  in  which  man  may  hope  to 
navigate  the  air.  He  may  imitate  the  flight  of  birds  with  a machine 
with  moving  or  flapping  wings;  he  may  use  vertical  screws  or  helices 
to  pull  himself  up;  he  may  use  an  aeroplane  and  sail  the  air  like  an 
eagle;  or,  lastly,  he  may  raise  himself  by  means  of  a gas  bag  and 
either  drift  with  the  wind  or  move  forward  by  means  of  propellers. 

In  these  attempts,  apparatus  of  several  different  types  has  been 
developed.  The  types  are  classed  in  two  general  divisions  based 
on  their  weight  relative  to  that  of  the  atmosphere,  viz,  the  lighter- 


DIRIGIBLE  BALLOONS 


3 


than-air  machines  and  the  heavier-than-air  machines.  Lighter-than- 
air  machines  are  those  which  employ  a bag  filled  with  a gas  whose 
specific  gravity  is  sufficiently  less  than  that  of  the  air  to  lift  the  bag 
and  the  necessary  attachments  from  the  earth,  and  include  simple 
balloons  and  dirigibles.  Heavier-than-air  machines,  which  will 
neither  rise  nor  remain  in  the  air  without  motive  power,  include  all 
forms  of  aeroplanes. 


SIMPLE  BALLOONS 

Theory.  The  balloon-like  airship  has  been  more  highly  developed 
than  any  other  type  of  aerial  craft,  probably  because  it  offers  the 
most  obvious  means  of  overcoming  the  force  of  gravitation.  It 
depends  on  the  law  of  Archimedes: 

“Every  body  which  is  immersed  in  a fluid  is  acted  upon  by  an 
upward  force,  exactly  equal  to  the  weight  of  the  fluid  displaced  by  the 
immersed  body.” 

That  is,  a body  will  be  at  rest  if  immersed  in  a fluid  of  equal 
specific  gravity  or  equal  weight,  volume  for  volume;  if  the  body  has 
less  specific  gravity  than  the  fluid  in  which  it  is  immersed  it  will 
rise;  if  it  has  a greater  specific  gravity  it  will  sink.  Therefore,  if 
the  total  weight  of  a balloon  is  less  than  the  weight  of  all  the  air  it 
displaces  it  will  rise  in  the  air.  It  is,  then,  necessary  to  fill  the  balloon 
with  some  gas  whose  specific  gravity  is  enough  less  than,  that  of  the 
air  to  make  the  weight-  of  the  gas  itself,  the  bags,  and  the  attach- 
ments, less  than  the  weight  of  the  air  displaced  by  the  whole  appa- 
ratus. The  gases  usually  employed  are  hydrogen,  coal  gas,  and  hot 
air. 

At  atmospheric  pressure  and  freezing  temperature,  the  weight 
of  a cubic -foot  of  air  is  about  .08  pound;  the  weight  of  a cubic  foot 
of  hydrogen  is  about  .005  pound,  under  the  same  conditions.  Accord- 
ing to  the  law  of  Archimedes,  a cubic  foot  of  hydrogen  would  be 
acted  upon  by  a force  equal  to  the  difference,  or  approximately  .075 
pound,  tending  to  move  it  upwards.  In  the  same  way,  a cubic  foot 
of  coal  gas,  which  weighs  .04  pound,  would  be  acted  upon  by  an 
upward  force  of  .04  pound. 

It  is  evident,  then,  that  a considerable  volume  of  gas  is  required 
to  lift  a balloon  with  its  envelope,  net,  car,  and  other  attachments. 


4 


DIRIGIBLE  BALLOONS 


Further,  it  requires  almost  twice  as  much  coal  gas  as  hydrogen, 
under  the  same  conditions,  for  we  have  seen  that  the  upward  force 
on  it  is  only  half  as  great.  The  lifting  power  of  hot  air  is  less  than 
one-eighth  as  great  as  that  of  hydrogen  at  the  highest  temperature 

that  can  possibly  be  used  in  a 
balloon. 

The  general  type  of  lighter- 
than-air  machines  may  be  divided 
into  aerostats  (ordinary  balloons, 
which  are  entirely  dependent  on 
wind  currents  for  lateral  move- 
ment, and  which  are  often  the 
chief  features  at  country  fairs) 
and  dirigible  balloons  or  aeronats 
(air  swimmers).  Dirigible  bal- 
loons employ  the  gas  bag  for 
maintaining  buoyancy,  and  have 
rudders  to  guide  them  and  pro- 
pellers to  drive  them  forward 
through  the  air  in  much  the 
same  way  that  ships  are  driven 
through  the  water. 

The  First  Balloon.  For  several 
years,  Joseph  and  Steven  Mont- 
golfier had  been  experimenting 
with  a view  to  constructing  a bal- 
loon: in  the  first  place  by  filling 
bags  with  steam;  then  by  filling 
bags  with  smoke,  and  finally  by 
filling  bags  with  hydrogen.  These  attempts  were  all  failures,  for  the 
steam  rapidly  condensed  and  the  smoke  and  hydrogen  leaked  through 
the  pores  in  the  bags.  They  finally  hit  upon  the  idea  of  filling  the 
bag  with  hot  air,  by  means  of  a fire  under  its  open  mouth.  Several 
balloons  were  burned  up,  but  the  next  was  always  made  larger,  until, 
at  their  first  public  exhibition  on  June  5,  1783,  the  bag  had  become 
over  35  feet  in  diameter.  On  this  occasion,  it  rose  to  a height  of 
between  900  and  1,000  feet,  but  the  hot  air  was  gradually  escaping, 
and  at  the  end  of  ten  minutes  the  balloon  fell  to  the  ground. 


Fig.  3.  Montgolfier  Balloon 


DIRIGIBLE  BALLOONS 


5 


The  Montgolfiers  then  went  to  Paris,  where,  after  suffering 
the  loss  of  a paper  balloon  by  rain,  they  sent  up  a waterproofed  linen 
one  carrying  a sheep,  a duck,  and  a rooster  in  a basket.  A rupture  in 
the  linen  caused  the  three  unwilling  aeronauts  to  make  a landing 
at  the  end  of  about  ten  minutes.  The  Montgolfiers  received  great 
honor,  and  small  balloons  of  this  type  became  a popular  fad.  One 
of  these  balloons  is  shown  in  Fig.  3,  making  an  ascension. 

Rozier.  The  first  man  to  go  up  in  a balloon  was  Rozier,  who 
ascended  in  a captive  balloon  to  a height  of  about  80  feet,  in  the 
latter  part  of  the  year  1783.  Later,  in 
company  with  a companion,  he  made  a 
voyage  in  a free  balloon,  remaining  in  the 
air  about  half  an  hour.  In  these  balloons, 
the  air  within  was  kept  hot  by  means  of 
a fire  carried  in  a pan  immediately  below 
the  mouth  of  the  bag,  as  shown  in  Fig.  4. 

Accidents  were  numerous  on  account  of 
the  fabric  becoming  ignited  from  the  fire 
in  the  pan. 

Improvements  by  Charles.  The  phys- 
icist, Charles,  was  working  along  these  lines 
at  the  same  time.  He  coated  his  balloon 
with  a rubber  solution  to  close  up  the 
pores,  and  was  thereby  enabled  to  sub- 
stitute hydrogen  for  the  hot  air.  Shortly 
after  the  Montgolfiers’  first  public  exhibi- 
tion, Charles  sent  up  his  balloon  for  the  benefit  of  the  Academie  des 
Sciences  in  Paris.  The  balloon,  which  weighed  about  19  pounds, 
ascended  rapidly  in  the  air  and  disappeared  in  the  clouds,  where  it 
burst  and  fell  in  a suburb  of  the  city.  The  impression  produced  upon 
the  peasants  at  seeing  it  fall  from  the  heavens  was  hardly  different 
from  what  could  be  expected.  They  believed  it  to  be  of  devilish  ori- 
gin, and  immediately  tore  it  into  shreds.  Charles  subsequently  built  a 
large  balloon  quite  similar  to  those  in  use  today.  A net  was  used  to 
support  the  basket,  and  a valve,  operated  by  means  of  ropes  from  the 
basket,  was  arranged  at  the  top  to  permit  the  gas  to  escape  as  desired. 

The  Balloon  Successful.  The  English  Channel  was  first  crossed 
in  1785.  Blanchard,  an  Englishman,  and  Jeffries,  an  American, 


Fig.  4.  Rozier  Hot-Air  Balloon 


6 


DIRIGIBLE  BALLOONS 


started  from  Dover  on  January  7 in  a balloon  equipped  with  wings 
and  oars.  After  a very  hazardous  voyage,  during  which  they  had 
to  cast  overboard  everything  movable  to  keep  from  drowning,  they 
landed  in  triumph  on  the  French  coast. 

An  attempt  to  duplicate  this  feat  was  made  shortly  afterward  by 
Rozier.  He  constructed  a balloon  filled  with  hydrogen,  below  which 
hung  a receiver  in  which  air  could  be  heated.  He  hoped  to  replace 
by  the  hot  air  the  losses  due  to  leakage  of  hydrogen.  Soon  after  the 
start  the  balloon  exploded,  due  to  the  escaping  gas  reaching  the  fire, 
and  Rozier  and  his  companion  were  dashed  on  the  cliffs  and  killed. 

EARLY  DIRIGIBLES 

Meusnier  the  Pioneer.  The  fact  that  the  invention  of  the 
dirigible  balloon  and  means  of  navigating  it  were  almost  simultane- 
ous is  very  little  known  today  and  much  less  appreciated.  Like 
the  aeroplane,  its  development  was  very  much  retarded  by  the  lack 
of  suitable  means  of  propulsion,  and  the  actual  history  of  what  has 
been  accomplished  in  this  field  dates  back  only  to  the  initial  circular 
flight  of  La  France  in  1885.  Still  the  principles  upon  which  success 
has  been  achieved  were  laid  down  within  a year  of  the  appearance 
of  Montgolfier’s  first  gas  bag.  Lieutenant  Meusnier,  who  subse- 
quently became  a general  in  the  French  army,  must  really  be  credited 
with  being  the  true  inventor  of  aerial  navigation.  At  a time  when 
nothing  whatever  was  known  of  the  science,  Meusnier  had  the  dis- 
tinction of  elaborating  at  one  stroke  all  the  laws  governing  the 
stability  of  an  airship,  and  calculating  correctly  the  conditions  of 
equilibrium  for  an  elongated  balloon,  after  having  strikingly  demon- 
strated the  necessity  for  this  elongation.  This  was  in  178-1  and  Meus- 
nier’s  designs  and  calculations  are  still  preserved  in  the  engineering 
section  of  the  French  War  Office  in  the  form  of  drawings  and  tables. 

But  as  often  proved  to  be  the  case  in  other  fields  of  research, 
his  efforts  went  unheeded.  How  marvelous  the  establishment  of 
these  numerous  principles  by  one  man  in  a short  time  really  is,  can 
be  appreciated  only  by  noting  the  painfully  slow  process  that  has 
been  necessary  to  again  determine  them,  one  by  one,  at  considerable 
intervals  and  after  numerous  failures.  Through  not  following  the 
lines  which  he  laid  down,  aerial  navigation  lost  a century  in  futile 
groping  about;  in  experiments  absolutely  without  method  or  sequence. 


DIRIGIBLE  BALLOONS 


7 


Meusnier’s  designs  covered  two  dirigible  balloons  and  that  he 
fully  appreciated  the  necessity  for  size  is  shown  by  the  dimensions 
of  the  larger,  which  unfortunately  was  never  built.  This  was  to  be 
260  feet  long  by  130  feet  in  diameter,  in  the  form  of  an  ellipse,  the 
elongation  being  exactly  twice  the  diameter.  In  other  words,  a perfect 
ellipsoid,  which  was  a logical  and,  in  fact,  the  most  perfect  develop- 
ment of  the  spherical  form.  Although  increased  knowledge  of  wind 
resistance  and  the  importance  of  the  part  it  plays  has  proved  'his 
relative  dimensions  to  be  faulty,  a study  of  the  principal  features 


Fig.  5.  Meusnier  Dirigible  Balloon 

of  his  machine  shows  that  he  anticipated  the  present-day  dirigible 
of  the  most  successful  type  at  practically  every  point,  barring,  of 
course,  the  motive  power,  as  there  was  absolutely  nothing  available 
in  that  day  except  human  effort.  As  the  latter  weighs  more  than 
one-half  ton  per  horse-power,  it  goes  without  saying  that  Meusnier’s 
balloon  would  have  been  dirigible  only  in  a dead  calm. 

He  adopted  the  elongated  form,  conceived  the  girth  fastening, 
the  triangular  or  indeformable  suspension,  the  air  balloonet  and  its 
pumps,  and  the  screw  propeller,  all  of  which  are  to  be  found  in  the 
dirigibles  of  present-day  French  construction,  Fig.  5.  It  need  scarcely 


8 


DIRIGIBLE  BALLOONS 


be  added  that  the  French  have  not  only  devoted  a greater  amount 
of  time  and  effort  to  the  development  of  the  dirigible  than  any  other 
nation,  but  have  also  met  with  the  greatest  success  in  its  use.  It 
was  not  until  1886,  or  more  than  a century  after  Meusnier  had  first 
elaborated  those  principles,  that  their  value  became  known.  They 
were  set  forth  by  Lieutenant  Letourne,  of  the  French  engineers,  in 
a paper  presented  to  the  Academic  des  Sciences  by  General  Perrier. 

In  one  form  or  another,  the  salient  features  of  Meusnier’s  diri- 
gible will  be  found  embodied  in  the  majority  of  attempts  of  later 
days.  His  large  airship  was  designed  to  consist  of  double  envelope, 
the  outer  container  of  which  was  to  provide  the  strength  necessary, 
and  it  was  accordingly  reinforced  by  bands.  The  inner  envelope  was 
to  provide  the  container  for  the  gas  and  was  not  called  upon  to  sup- 
port any  weight.  This  inner  bag  or  balloon  proper  was  designed 
to  be  only  partially  inflated  and  the  space  between,  the  two  was  to  be 
occupied  by  air  which  could  be  forced  into  it  at  two  points  at  either 
end,  by  pumps,  so  as  to  maintain  the  pressure  on  the  gas  bag  uniform 
regardless  of  the  expansion  or  contraction  of  its  contents.  Here  in 
principle  was  the  air  balloonet  of  today.  Instead  of  employing  a net 
to  hang  the  car  from  the  outer  envelope,  the  former  was  attached 
by  means  of  a triangular  suspension  system  fastened  to  a heavy  rope 
band,  or  girth,  encircling  the  outer  envelope.  At  the  three  points 
where  the  lifting  rope  members  met,  a shaft  running  the  length  of 
the  car  and  carrying  what  Meusnier  described  as  “revolving  oars” 
was  installed.  These  constituted  the  prototype  of  the  screw  pro- 
peller, invented  for  aerial  navigation  at  a time  long  antedating  the 
use  of  steam  for  marine  use.  Thus  he  devised:  (1)  The  air  balloonet 
to  husband  the  gas  supply  and  thus  prevent  the  deformation  of  the 
outer  container  or  support,  as  well  as  to  provide  stability;  (2)  the 
triangular  suspension  to  attain  longitudinal  stability;  and  (3)  the 
screw  propeller  for  propulsion,  beside  selecting  the  proper  location 
for  the  latter. 

PROBLEMS  OF  THE  DIRIGIBLE 

Ability  to  Float.  If  ability  to  rise  in  the  air  depended  merely 
upon  a knowledge  of  the  principle  that  made  it  possible,  it  undoubt- 
edly would  have  been  accomplished  many  centuries  ago.  As  already 


DIRIGIBLE  BALLOONS 


9 


mentioned,  Archimedes  established  the  fact  that  a body  upon  float- 
ing in  a fluid  displaces  an  amount  of  the  latter  equal  in  weight  to 
the  body  itself,  and  upon  this  theory  was  formulated  the  now  well- 
known  law,  that  every  body  plunged  into  a fluid  is  subjected  by  this 
fluid  to  a pressure  from  below,  equivalent  to  the  weight  of  the  fluid 
displaced  by  the  body.  Consequently,  if  the  weight  of  the  latter 
be  less  than  that  of  the  fluid  it  displaces,  the  body  will  float.  It  is 
by  reason  of  this  that  the  iron  ship  floats  and  the  fish  swims  in  water. 
If  the  weight  of  the  body  and  the  displaced  water  be  the  same,  the 
body  will  remain  in  equilibrium  in  the  water  at  a certain  level,  and 
if  that  of  the  body  be  greater,  it  will  sink.  All  three  of  these  factors 
are  found  in  the  fish,  which,  with  the  aid  of  its  natatory  gland,  can 
rise  to  the  surface,  sink  to  the  bottom,  or  remain  suspended  at  differ- 
ent levels.  To  accomplish  these  changes  of  specific  gravity,  the  fish 
fills  this  gland  with  air,  dilating  it  until  full,  or  compressing  and 
emptying  it.  In  this  we  find  a perfect  analogy  to  the  air  balloonet 
of  the  dirigible,  which  serves  the  same  purposes.  The  method  by 
which  lifting  power  is  obtained  in  the  dirigible  is  exactly  the  same 
as  in  the  case  of  the  balloon. 

But  once  in  the  air,  a balloon  is,  to  all  intents  and  purposes, 
a part  of  the  atmosphere.  There  is  absolutely  no  sensation  of  move- 
ment, either  vertically  or  horizontally.  The  earth  appears  to  drop 
away  from  beneath  and  to  sweep  by  horizontally,  and  regardless  of 
how  violently  the  wind  may  be  blowing,  the  balloon  is  always  in  a 
dead  calm  because  it  is  really  part  of  the  wind  itself  and  is  traveling 
with  it  at  exactly  the  same  speed.  If  it  were  not  for  the  loss  of  lift- 
ing power  through  the  expansion  and  contraction  of  the  gas,  making 
it  necessary  to  permit  its  escape' in  order  to  avoid  rising  to  incon- 
venient heights  on  a very  warm  day,  and  the  sacrifice  of  ballast  to 
prevent  coming  to  earth  at  night,  the  ability  of  a balloon  to  stay  up 
would  be  limited  only  by  the  endurance  of  its  crew  and  the  quantity 
of  provisions  it  was  able  to  transport.  As  the  use  of  air  balloonets 
in  the  dirigible  takes  care  of  this,  the  question  of  lifting  power  presents 
no  particular  difficulty.  It  is  only  a matter  of  providing  sufficient 
gas  to  support  the  increased  weight  of  the  car,  motor  and  its  acces- 
sories, and  the  crew  of  the  larger  vessel,  with  a factor  of  safety  to 
allow  for  emergencies,  in  order  to  permit  of  staying  in  the  air  long 
enough  to  make  a protracted  voyage. 


10 


DIRIGIBLE  BALLOONS 


Air  Resistance  vs.  Speed.  Unless  a voyage  is  to  be  governed 
in  its  direction  entirely  by  the  wind,  the  dirigible  must  possess  a 
means  of  moving  contrary  to  the  latter.  The  moment  this  is 
attempted,  resistance  is  encountered,  and  it  is  this  resistance  of  the 
air  that  is  responsible  for  the  chief  difficulties  in  the  design  of  the 
dirigible.  To  drive  it  against  the  wind,  it  must  have  power;  to  sup- 
port the  weight  of  the  motor  necessary,  the  size  of  the  gas  bag  must 
be  increased.  But  with  the  increase  in  size,  the  amount  of  resistance' 
is  greatly  multiplied  and  the  power  to  force  it  through  the  air  must 
be  increased  correspondingly.  The  law  is  approximately  as  follows: 

Where  the  surface  moves  in  a line  'perpendicular  to  its  plane,  the 
resistance  is  proportional  to  the  extent  of  the  surface,  to  the  square  of 
the  speed  with' which  the  surface  is  moved  through  the  air,  and  to  a 
coefficient,  the  mean  value  of  ivhich  is  0.125. 

This  coefficient  is  a doubtful  factor,  the  figure  given  having  been 
worked  out  years  ago  in  connection  with  the  propulsion  of  sailing 
vessels.  Its  value  varies  according  to  later  experimenters  between 
.08  and  .It),  the  mean  of  the  more  recent  investigations  of  Renard, 
Eiffel,  and  others  who  have  devoted  considerable  study  to  the  matter, 
being  .08.  This  is  dwelt  upon  more  in  detail  under  “Aerodynamics” 
and  it  will  be  noted  that  the  values  of  the  coefficient  K,  given  here, 
do  not  agree  with  those  stated  in  that  article.  They  serve,  how- 
ever, to  illustrate  the  principles  in  question. 

In  accordance  with  this  law,  doubling  the  speed  means  quad- 
rupling the  resistance  of  the  air.  For  instance,  a surface  of  16  square 
feet  moving  directly  against  the  air  at  a speed  of  10  feet  per  second 
will  encounter  a resistance  of  16X100  (square  of  the  speed)  X0.125 
= 200  pounds  pressure.  Doubling  the  speed,  thus  bringing  it  up 
to  20  feet  per  second,  would  give  the  equation  16  X 400  X 0.125  = 800 
pounds  pressure,  or  with  the  more  recent  value  of  the  coefficient 
of  .08,  512  pounds  pressure.  The  first  consideration  is  accord- 
ingly to  reduce  the  amount  of  surface  moving  at  right  angles.  The 
resistance  of  a surface  having  tapering  sides  which  cut  through  or 
divide  the  molecules  of  air  instead  of  allowing  them  to  impinge 
directly  upon  it,  is  greatly  diminished;  hence,  Meusnier’s  principle 
of  elongation.  If  we  take  the  same  panel  presenting  16  square  feet 
of  surface  and  build  out. on  it  a hemisphere,  its  resistance  at  a speed 
of  10  feet  per  second  will  be  exactly  half,  or  a pressure  of  100  pounds. 


DIRIGIBLE  BALLOONS 


11 


By  further  modifying  this  so  as  to  represent  a sharp  point,  or  acute- 
angled  cone,  it  will  be  38  pounds.  There  could  accordingly  be  no 
question  of  attempting 
to  propel  a spherical 
balloon. 

It  is  necessary  to 
select  a form  that  pre- 
sents as  small  a surface 
as  possible  to  the  air  as 
the  balloon  advances, 
while  preserving  the  max- 
imum lifting  power.  But 
experience  has  strikingly 
demonstrated  the  analogy  between  marine  and  aerial  practice — not 
only  is  the  shape  of  the  bow  of  the  vessel  of  great  importance  but, 
likewise,  the  stern.  The  profile  of  the  latter  may  permit  of  an  easy 
reunion  of  the  molecules  of  air  separated  by  the  former,  or  it  may 
allow  them  to  come  together  again  suddenly,  clashing  with  one  an- 
other and  producing  disturbing  eddies  just  behind  the  moving  body. 
To  carry  the  comparison  with  a marine  vessel  a bit  further,  the  form 
must  be  such  as  to  give  an  easy  “shear,”  or  sweep  from  stem  to 
stern. 


y j. 

6.  Giffard  Dirigible 


That  early  investi- 
gators appreciated  this  is 
shown  by  the  fact  that 
Giffard  in  1852,  Fig.  6, 

De  Lome  in  1872,  Fig.  7, 

Tissandier  in  1884,  and 
Santos-Dumont  in  his 
numerous  attempts,  a- 
dopted  a spindle-shaped 
or  “fusiform”  balloon.  In 
other  words,  their  shape, 
equally  pointed  at  either 
end,  was  symmetrical  in 
relation  to  their  central  plan, 
adapted  to  the  requirements  of  the  bow  did  not  serve  equally  well 
for  the  stern,  was  demonstrated  for  the  first  time  by  Renard,  to 


Fig.  7.  De  Lome  Dirigible 

However,  that  the  shape  best 


12 


DIRIGIBLE  BALLOONS 


whom  credit  must  be  given  for  a very  large  part  of  the  scientific 
development  of  the  dirigible.  Almost  a century  earlier,  Marey- 
Monge  had  laid  down  the  principle  that  to  be  successfully  pro- 
pelled through  the  air,  the  balloon  must  have  “the  head  of  a cod 
and  the  tail  of  a mackerel.”  Nature  exemplifies  the  truth  of  this 
in  all  swiftly  moving  fishes  and  birds.  Renard  accordingly  adopted 
what  may  best  be  termed  the  “piseiform”  type,  viz,  that  of  a dis- 
symmetrical fish  with  the  larger  ehd  serving  as  the  bow;  and  the 
performances  of  the  Renard,  Lebaudy,  and  Clement-Bayard  airships 
have  shown  that  this  is  the  most  advantageous  form. 

The  pointed  stern  prevents  the  formation  of  eddies  and  the 
creation  of  a partial  vacuum  in  the  wake  which  would  impose  addi- 
tional thrust  on  the  bow.  Zeppelin  has  disregarded  this  factor  by 
adhering  to  the  purely  cylindrical  form  with  short  hemispherical 
bow  and  stern,  but  it  is  to  be  noted  that  while  other  German  inves- 
tigators originally  followed  this  precedent,  they  have  gradually 
abandoned  it,  owing  to  the  noticeable  retarding  effect. 

Critical  Size  of  Bag.  Next  in  importance  to  the  best  form  to 
be  given  the  vessel,  is  the  most  effective  size — something  which  has 
a direct  bearing  upon  its  lifting  power.  This  depends  upon  the 
volume,  while  the  resistance  is  proportional  to  the  amount  of  sur- 
face presented.  Greater  lifting  power  can  accordingly  be  obtained 
by  keeping  the  diameter  down  and  increasing  the  length.  But  the 
resistance  is  also  proportionate  to  the  square  of  the  speed,  while 
the  volume,  or  lifting  power,  varies  as  the  cube  of  the  dimensions 
of  the  container,  so  that  in  doubling  the  latter,  the  resistance  of  the 
vessel  at  a certain  speed  is  increased  only  four  times  while  its  lifting 
capacity  is  increased  eight  times.  Consequently  the  larger  dirigible 
is  very  much  more  efficient  than  the  smaller  one  since  it  can  carry 
so  much  more  weight  in  the  form  of  a motor  and  fuel  in  proportion 
to  its  resistance  to  the  air.  As  an  illustration  of  this,  assume  a rec- 
tangular container  with  square  ends  1 foot  each  way  and  5 feet  long. 
Its  volume  will  be  5 cubic  feet  and  if  the  lifting  power  of  the  gas  be 
assumed  as  2 pounds  per  cubic  foot,  its  total  lifting  power  will  be  5 
pounds.  If  a motor  weighing  exactly  5 pounds  per  horse-power 
be  assumed,  it  will  be  evident  that  the  motor  which  such  a balloon 
could  carry  would  be  limited  to  1 horse-power,  neglecting  the  weight 
of  the  container. 


DIRIGIBLE  BALLOONS 


13 


Double  these  dimensions  and  the  container  will  then  measure 
2X2X 10  feet,  giving  a volume  of  40  cubic  feet,  and  a lifting  power,  on 
the  basis  already  assumed,  of  a motor  capable  of  producing  8 horse- 
power, and  this  without  taking  into  consideration  that  as  the  size 
of  the  motor  increases,  its  weight  per  horse-power  decreases.  The 
balloon  of  twice  the  size  will  thus  have  a motor  of  8 horse-power  to 
overcome  the  resistance  of  the  head-on  surface  of  4 square  feet,  or 
2 horse-power  per  square  foot  of  transverse  section,  whereas  the 
balloon  of  half  the  size  will  have  only  1 horse-power  per  square  foot 
of  transverse  section.  It  is,  accordingly,  not  practicable  to  construct 
small  dirigibles  such  as  the  various  airships  built  by  Santos-Dumont 
for  his  experiments,  while,  on  the  other  hand,  there  are  numerous 
limitations  that  will  be  obvious,  restricting  an  increase  in  size  beyond 
a certain  point,  as  has  been  shown  by  the  experience  of*  the  various 
Zeppelin  airships. 

To  make  it  serviceable,  what  Berget  terms  the  “independent 
speed’’  of  a dirigible,  i.e.,  its  power  to  move  itself  against  the  wind, 
must  be  sufficient  to  enable  it  to  travel  finder  normally  prevailing 
atmospheric  conditions.  These  naturally  differ  greatly  in  different 
countries  and  in  different  parts  of  the  same  country.  Where  mete- 
orological tables  showed  the  prevailing  winds  in  a certain  district 
to  exceed  15  miles  an  hour  throughout  a large  part  of  the  year,  it 
would  be  useless  to  construct  an  airship  with  a speed  of  15  miles 
an  hour  or  less  for  use  in  that  particular  district,  as  the  number 
of  days  in  the  year  in  which  one  could  travel  to  and  from  a certain 
starting  point  would  be  limited.  This  introduces  another  factor 
which  has  a vital  bearing  upon  the  size  of  the  vessel.  Refer  to  the 
figures  just  cited  and  assume  further  that  by  doubling  the  dimensions 
and  making  the  airship  capable  of  transporting  a motor  of  8 horse- 
power, it  has  a speed  of  10  miles  an  hour.  It  is  desired  to  double  this. 
But  the  resistance  of  the  surface  presented  increases  as  the  square  of 
the  speed.  Hence,  it  will  not  avail  merely  to  double  the  power  of 
the  motor.  Experience  has  demonstrated  that  the  power  necessary 
to  increase  the  speed  of  the  same  body,  increases  in  proportion  to 
the  cube  of  the  speed,  so  that  instead  of  a 16-horse-power  motor  in  the 
case  mentioned,  one  of  64  horse-power  would  be  needed.  There  are, 
accordingly,  a number  of  elements  that  must  be  taken  into  considera- 
tion when  determining  the  size  as  well  as  the  shape  of  the  balloon. 


14 


DIRIGIBLE  BALLOONS 


Static  Equilibrium.  Having  settled  upon  the  size  and  shape, 
there  must  be  an  appropriate  means  of  attaching  the  car  to  carry 
the  power  plant,  its  accessories  and  control,  and  the  crew.  While 
apparently  a simple  matter,  this  involves  one  of  the  most  important 
elements  of  the  design — that  of  stability.  A long  envelope  of  com- 
paratively small  diameter  being  necessary  for  the  reasons  given, 
it  is  essential  that  this  be  maintained  with  its  axis  horizontal.  In 
calm  air,  the  balloon,  or  container,  is  subjected  to  the  action  of 
two  forces:  One  is  its  weight',  applied  to  the  center  of  gravity  of 
the  system  formed  by  the  balloon,  its  car,  and  all  the  supports; 
the  other  is  the  thrust  of  the  air,  applied  at  a point  known  as  the 
center  of  thrust  and  which  will  differ  with  different  designs,  accord- 
ing as  the  car  is  suspended  nearer  or  farther  away  from  the  balloon. 
If  the  latter  contained  only  the  gas  used  to  inflate  it,  with  no  car 
or  other  weight  to  carry,  the  center  of  gravity  and  the  center  of 
thrust  would  coincide,  granting  that  the  weight  of  the  envelope  were 
negligible.  As  this  naturally  can  not  be  the  case,  these  forces  are 
not  a continuation  of  each  other.  But  as  they  must  necessarily  be 
equal  if  the  balloon  is  neither  ascending  nor  descending,  it  follows 
that  they  will  cause  the  balloon  to  turn  until  they  are  a continua- 
tion of  each  other,  and  in  the  case  of  a pisciform  balloon,  this  will 
cause  it  to  tilt  downward.  Like  a ship  with  too  much  cargo  for- 
ward, it  would  be  what  sailors  term  “down  at  the  head.” 

As  this  would  be  neither  convenient  nor  compatible  with  rapid 
propulsion,  it  must  be  avoided  by  distributing  the  weight  along  the 
car  in  such  a manner  that  when  the  balloon  is  horizontal,  the  forces 
represented  by  the  pressure  above  and  the  weight  below,  must  be  in 
the  same  perpendicular.  This  is  necessary  to  insure  static  equilibrium, 
or  a horizontal  position  while  in  a state  of  rest.  To  bring  this  about, 
the  connections  between  the  car  and  the  balloon  must  always  main- 
tain the  same  relative  position,  which  is  further  complicated  by  the 
fact  that  they  must  be  flexible  at  the  same  time. 

Longitudinal  Stability.  But  the  longitudinal  stability  of  the 
airship  as  a whole  must  be  preserved,  and  this  also  involves  its 
stability  of  direction.  Its  axis  must  be  a tangent  to  the  course  it 
describes,  if  the  latter  be  curvilinear,  Or  parallel  with  the  direction 
of  this  course  where  the  course  itself  is  straight.  This  is  apparently 
something  which  should  be  taken  care  of  by  the  rudder,  any  ten- 


DIRIGIBLE  BALLOONS 


15 


dency  on  the  part  of  the  airship  to  diverge  from  its  course  being  cor- 
rected by  the  pilot.  But  a boat  that  needed  constant  attention  to 
the  helm  to  keep  it  on  its  course  would  be  put  down  as  a “cranky” 
— in  other  words,  of  faulty  design  in  the  hull.  A dirigible  having 
the  same  defect  would  be  difficult  to  navigate,  as  the  rudder  alone 
would  not  suffice  to  correct  this  tendency  in  emergencies.  Stability 
of  direction  is,  accordingly,  provided  for  in  the  design  of  the  balloon 
itself,  and  this  is  the  chief  reason  for  adopting  the  form  of  a large- 
headed and  slender-bodied  fish,  as  already  outlined.  This  brings 
the  center  of  gravity  forward  and  makes  of  the  long  tail  an  effective 
lever  which  overcomes  any  tendency  of  the  ship  to  diverge  from  the 
course  it  should  follow,  by  causing  the  resistance  of  the  air  itself  to 
bring  it  back  into  line.  Howeyer,  the  envelope  of  the  balloon  itself 
would  not  suffice  for  this,  so  just  astern  of  the  latter,  “stabilizing 
surfaces”are  placed, consisting  of  vertical  planes  fixed  to  the  envelope. 
These  form  the  keel  of  the  dirigible  and  are  analogous  to  the  keel  of 
the  ship.  Stability  of  direction  is  thus  obtained  naturally  without 
having  constant  recourse  to  the  rudder,  which  is  employed  only 
to  alter  the  direction  of  travel. 

The  comparison  between  marine  and  aerial  navigation  must  be 
carried  even  further.  These  vertical  planes,  or  “keel,”  prevent 
rolling;  it  is  equally  necessary  to  avoid  pitching — far  more  so  than 
in  the  case  of  a vessel  in  water.  So  that  while  the  question  of  sta- 
bility of  direction  is  intimately  connected  with  longitudinal  stability, 
other  means  are  required  to  insure  the  latter.  The  airship  must 
travel  on  an  “even  keel,”  except  when  ascending  or  descending, 
and  the  latter  must  be  closely  under  the  control  of  the  pilot,  as 
otherwise  the  balloon  may  incline  at  a dangerous  angle.  This  shows 
the  importance  of  an  unvarying  connection  between  the  car  and  the 
envelope  to  avoid  defective  longitudinal  stability.  Assume,  for 
instance,  that  the  car  is  merely  attached  at  each  end  of  a single 
line.  The-  car,  the  horizontal  axis  of  the  balloon,  and  the  two  sup- 
ports would  then  form  a rectangle.  AYhen  in  a state  of  equilibrium 
the  weight  arid  the  thrust  are  acting  in  the  same  line.  Now  suppose 
that  the  pilot  desires  to  descend  and  inclines  the  ship  downward. 
The  center  of  gravity  is  then  shifted  farther  forward  and  the  two 
forces  are  no  longer  in  line. 

But  as  the  connections  permit  the  car  to  swing  in  a vertical 


16 


DIRIGIBLE  BALLOONS 


plane,  they  permit  the  latter  to  move  forward  and  parallel  with  the 
balloon,  thus  forming  a parallelogram  instead  of  a rectangle.  This 
causes  the  center  of  gravity  to  shift  even  farther,  and  as  one  of  the 
most  serious  causes  of  longitudinal  stability  is  the  movement  of  the 
gas  itself,  it  would  also  rush  to  the  back  end  and  cause  the  balloon 
to  “stand  on  its  head.’’  As  the  tendency  of  the  gas  is  thus  to  aug- 
ment any  inclination  accidentally  produced,  the  vital  necessity  of 
providing  a suspension  that  is  incapable  of  displacement  with  rela- 
tion to  the  balloon  is  evident.  Here  is  where  the  importance  of  Meus- 
nier’s  conception  of  the  principle  of  triangular  suspension  comes  in. 
Instead  of  being  merely  supported  by  direct  vertical  connections 
with  the  balloon,  the  ends  of  the  car  are  also  attached  to  the 
opposite  ends  of  the  envelope,  forming  opposite  triangles.  This  gives 
an  unvarying  attachment,  so  that  when  the  balloon  inclines,  the  car 
maintains  its  relative  position,  and  the  weight  and  thrust  tend  to  pull 
each  other  back  in  the  same  line,  or,  in  other  words,  to  “trim  ship.” 
Dynamic  Equilibrium.  In  addition  to  being  able  to  preserve 
its  static  equilibrium  and  to  possess  proper  longitudinal  stability, 
the  successful  airship  must  also  maintain  its  dynamic  equilibrium — 
the  equilibrium  of  the  airship  in  motion.  This  may  be  made  clear 
by  referring  to  the  well-known  expedients  adopted  to  navigate 
the  ordinary  spherical  balloon.  To  rise,  its  weight  is  diminished  by 
gradually  pouring  sand  from  the  bags  which  are  always  carried  as 
ballast.  To  descend,  it  is  necessary  to  increase  the  total  weight  of 
the  balloon  and  its  car,  and  the  only  method  of  accomplishing  this 
is  to  permit  the  escape  of  some  of  the  gas,  the  specific  lightness 
of  which  constitutes  the  lifting  power  of  the  balloon.  As  the  gas 
escapes,  the  thrust  of  the  air  on  the  balloon  is  decreased  and  it 
sinks — the  ascensional  effort  diminishing  in  proportion  to  the 
amount  of  gas  that  is  lost.  The  balloon,  or  the  container  itself, 
being  merely  a spherical  bag,  on  the  upper  hemispherical  half  of 
which  the  net  supporting  the  car  presses  at  all  points,  the  question 
of  deformation  is  not  a serious  one.  Before  it  assumed  propor- 
tions where  the  bag  might  be  in  danger  of  collapsing,  the  balloon 
would  have  had  to  come  to  earth  through  lack  of  lifting  power 
to  longer  sustain  it.  Owing  to  its  far  greater  size,  as  well  as  to  the 
form  of  the  surface  which  it  presents  to  the  air  pressure,  such  a crude 
method  is  naturally  not  applicable  to  the  dirigible. 


DIRIGIBLE  BALLOONS 


17 


Dynamic  equilibrium  must  take  into  account  not  only  its  weight 
and  the  sustaining  pressure  of  the  air,  but  also  the  resistance  of  the 
air  exerted  upon  its  envelope.  This  resistance  depends  upon  the 
dimensions  and  the  shape  of  that  envelope,  and  in  calculations  the 
latter  is  always  assumed  to  be  invariable.  Assume,  for  instance, 
that  to  descend  the  pilot  of  a dirigible  allowed  some  of  the  hydrogen 
gas  to  escape.  As  the  airship  came  down,  it  would  have  to  pass 
through  strata  of  air  of  constantly  increasing  pressure  as  the  earth 
is  approached.  The  reason  for  this  will  be  apparent  as  the  lower 
strata  bear  the  weight  of  the  entire  atmosphere  above  them.  The 
confined  gas  will  no  longer  be  sufficient  t6  distend  the  envelope, 
the  latter  losing  its  shape  aiid  becoming  flabby.  As  the  original 
form  is  no  longer  retained,  the  center  of  resistance  of  the  air  will 
likewise  have  changed  together  with  the  center  of  thrust,  and  the 
initial  conditions  will  no  longer  obtain.  But  as  the  equilibrium  of 
the  airship  depends  upon  the  maintenance  of  these  conditions,  it 
will  be  lost  if  they  vary. 

Function  of  Balloonets.  In  the  function  of  balloonets  is  realized 
the  importance  of  the  principle  established  by  Meusnier.  It  was 
almost  a century  later  before  it  was  rediscovered  by  Dupuy  de  Lome 
in  connection  with  his  attempts  to  make  balloons  dirigible.  That 
the  balloon  must  always  be  maintained  in  a state  of  perfect  infla- 
tion has  been  pointed  out.  But  gas  is  lost  in  descents  and  to  a 
certain  extent,  through  the  permeability  of  the  envelope.  LTnless 
it  is  replaced,  the  balloon  will  be  only  partially  inflated.  In  view 
of  the  great  volume  necessary,  it  requires  no  explanation  to  show 
that  it  would  be  impossible  to  replace  the  gas  itself  by  fresh  hydrogen 
carried  on  the  car.  It  would  have  to  be  under  high  pressure  and 
the  weight  of  the  steel  cylinders  as  well  as  the  number  necessary  to 
transport  a sufficient  supply  would  be  prohibitive.  Hence,  Meus- 
nier conceived  the  idea  of  employing  air.  But  this  could  not  be 
pumped  directly  into  the  balloon  to  mix  with  the  hydrogen  gas, 
as  the  resulting  mixture  would  not  only  still  be  as  inflammable  as 
the  former  alone,  but  it  would  also  contain  sufficient  oxygen  to 
create  a very  powerful  and  infinitely  more  dangerous  explosive. 
This  led  to  the  adoption  of  the  air  balloonet. 

In  principle  the  balloonet  consists  of  dividing  the  interior  of  the 
envelope  into  two  cells,  the  larger  of  which  receives  the  light  gas 


18 


DIRIGIBLE  BALLOONS 


while  the  smaller  is  intended  to  hold  air  and  terminates  in  a tube 
extending  down  to  a pump  in  the  car.  In  other  words,  a fabric 
partition  adjacent  to  the  lower  part  of  the  envelope  inside  and  sub- 
ject to  deformation  at  will.  In  actual  practice  it  consists  of  a num- 
ber of  independent  cells  of  this  kind,  longitudinally  disposed  along 
the  lower  half  of  the  interior  of  the  envelope. 

When  the  balloon  is  completely  inflated  with  hydrogen,  as  at 
the  beginning  of  an  ascent,  these  balloonets  lie  flat  against  the  lower 
part  of  the  envelope,  exactly  like  a lining.  As  the  airship  rises,  the 
gas  expands  owing  to  the  reduction  in  atmospheric  pressure  at  a 
higher  altitude,  as  well  as  to  the  influence  of  heat.  With  the  increase 
in  pressure,  uniform  inflation  is  maintained  by  the  escape  of  a cer- 
tain amount  of  gas  through  the  automatic  valves  provided  for  the 
purpose.  Unless  this  took  place,  the  internal  pressure  might  assume 
proportions  placing  the  balloon  in  danger  of  blowing  up.  To  avoid 
this,  a pressure  gauge  communicating  with  the  gas  compartment 
is  one  of  the  most  important  instruments  on  the  control  board  of 
the  car,  and  should  its  reading  indicate  a failure  of  the  automatic 
valves,  the  pilot  must  reduce  the  pressure  by  operating  a hand 
valve.  But  as  the  car  descends,  the  increased  external  pressure 
causes  a recontraction  of  the  gas  until  it  no  longer  suffices  to  fill  the 
envelope.  To  replace  the  loss  the  air  pumps  are  utilized  to  force 
air  into  the  air  balloonets  until  the  sum  of  the  volumes  of  gas  and 
air  in  the  different  compartments  equals  the  original  volume.  In 
this  manner,  the  initial  conditions,  upon  which  the  equilibrium  of 
the  airship  is  based,  are  always  maintained. 

This  is  not  the  only  method  of  correcting  for  change  in  volume, 
nor  of  maintaining  the  longitudinal  stability  of  the  whole  fabric, 
the  importance  of  which  has  already  been  detailed,  but  experience 
has  shown  that  it  is  the  most  practical.  It  is  possible  to  give  the 
balloon  a rigid  frame  over  which  the  envelope  is  stretched  and  to 
attach  the  car  by  means  of  a rigid  metal  suspension,  as  in  the  various 
Zeppelin  airships,  or  to  take  it  semi-rigid,  as  in  the  Gross,  another 
German  type  in  which  Zeppelin’s  precedent  was  followed  only  in 
the  case  of  the  suspension.  To  prevent  deformation  by  this  means, 
the  balloon  is  provided  with  an  absolutely  rigid  skeleton  of  aluminum 
tubes.  This  framing  is  in  the  shape  of  a number  of  uniform  cylin- 
drical sections,  or  gas  compartments,  each  one  of  which  accom- 


DIRIGIBLE  BALLOONS 


19 


modates  an  independent  balloon,  while  over  the  entire  frame  a very 
strong  but  light  fabric  constituting  the  outer  or  protecting  envelope 
is  stretched  taut.  The  idea  of  the  numerous  independent  balloons 
is  to  insure  a high  factor  of  safety  as  the  loss  of  the  entire  contents 
of  two  or  three  of  them  through  accident  would  not  dangerously 
affect  the  lifting  power  of  the  whole.  The  numerous  wrecks  which 
attended  the  landings  of  these  huge  non-flexible  masses  during 
the  early  stages  of  their  development  led  to  the  provision  of  some 
form  of  shelter  wherever  they  were  expected  to  land.  Even  now, 
they  are  practically  unmanageable  in  the  air  during  a fierce  wind 
and  iiiust  be  allowed  to  sail  under  control  until  the  wind  has 
tpent  itself. 

The  system  of  air  balloonets  has  accordingly  been  adopted  by 
every  other  designer,  in  variously  modified  forms,  as  illustrated  by 
the  German  dirigible  Parseval,  in  which  but  two  air  bags  were 
employed,  one  at  either  end.  They  were  interconnected  by  an  external 
tube  to  which  the  air-pump  discharge  was  attached,  and  were  also 
operated  by  a counterbalancing  system  inside  the  gas  bag,  by  means 
of  which  the  inflation  of  one  balloonet,  as  the  after  one,  for  example, 
caused  the  collapse  of  the  other. 

Influence  of  Fish  Form  of  Bag.  But  a condition  of  dynamic 
equilibrium  can  not  be  obtained  with  the  combined  aid  of  the  pre- 
cautions already  noted  to  secure  longitudinal  stability  and  that  of 
the  air  balloonet  in  maintaining  uniform  inflation.  Why  this  is  so 
will  be  clear  from  a simple  example.  If  a simple  fusiform  or  spindle- 
shaped  balloon  be  suspended  in  the  air  in  a horizontal  plane,  the 
axis  of  which  passes  through  its  center  of  gravity,  it  would  be  prac- 
tically pivoted  on  the  latter  and  would  be  extremely  sensitive  to 
influences  tending  to  tilt  it  up  or  down.  It  would  be  in  a state  of 
“indifferent”  longitudinal  equilibrium.  As  long  as  the  axis  of  the  bal- 
loon remains  horizontal  and  the  air  pressure  is  coincident  with  that 
axis,  it  will  be  in  equilibrium,  but  an  equilibrium  essentially  unstable. 
Experiment  proves  that  the  moment  the  balloon  inclines  from 
the  horizontal  in  the  slightest  degree,  there  is  a strong  tendency 
for  it  to  revolve  about  its  center  of  gravity  until  it  stands  vertical 
to  the  air  current,  or  is  standing  straight  up  and  down.  This,  of 
course,  refers  to  the  balloon  alone  without  any  attachments.  Such 
a tendency  would  be  fatal,  amounting  as  it  does  to  absolute  instability. 


20 


DIRIGIBLE  BALLOONS 


If  instead  of  symmetrical  form,  tapering  toward  both  ends,  a 
pisciform  balloon  be  tried,  it  will  still  evidence  the  same  tendency, 
but  in  greatly  diminished  degree.  This  is  not  merely  the  theory 
affecting  its  stability  but  represents  the  findings  of  Col.  Charles 
Renard,  who  undoubtedly  did  more  to  formulate  the  exact  laws 
governing  the  stability  of  a dirigible  than  any  other  investigator  in 
this  field.  His  data  is  the  result  of  a long  and  methodically  carried 
out  series  of  experiments.  In  the  case  of  the  pisciform  balloon,  the 
disturbing  effect  is  due  in  unequal  degree,  to  the  diameter  of  the 
balloon  and  its  inclination  and  speed,  whereas  the  steadying  effect 
depends  upon  the  inclination  and  diameter,  but  not  on  the  Speed. 
The  disturbing  effect,  therefore,  depends  solely  on  the  speed  and 
augments  very  rapidly  as  the  speed  increases.  It  will,  accordingly, 
be  apparent  that  there  is  a certain  speed  for  which  the  two  effects 
are  equal,  and  beyond  which  the  disturbing  influence,  depending  on 
speed,  will  overcome  the  steadying  effect. 

To  this  rate  of  travel,  Renard  applied  the  term  “critical  speed,” 
and  when  this  is  exceeded  the  equilibrium  of  the  balloon  becomes 
unstable.  To  obtain  this  data,  keels  of  varying  shapes  and  dimen- 
sions were  submitted  to  the  action  of  a current  of  air,  the  force  of 
which  could  be  varied  at  will.  In  the  case  of  the  La  France,  the  first 
fish-shaped  dirigible,  the  critical  speed  was  found  to  be  10  meters, 
or  approximately  39  feet  per  second,  a speed  of  21.6  miles  per  hour, 
and  a 24-horse-power  motor  suffices  to  drive  the  airship  at  this  rate 
of  travel.  But  the  internal  combustion  motor  is  now  so  light  that 
a dirigible  of  this  type  could  easily  lift  a motor  capable  of  generating 
80  to  100  horse-power.  With  this  amount  of  power,  its  theoretic 
speed  would  be  50  per  cent  greater,  or  33  miles  an  hour.  But  this 
could  not  be  accomplished  in  practice  as  long  before  it  was  reached 
the  stability  would  become  precarious.  As  Colonel  Renard  observed 
in  the  instance  just  cited,  “If  the  balloon  were  provided  with  a 100- 
horse-power  motor,  the  first  24  horse-power  would  make  it  go  and 
the  other  76  horse-power  would  break  our  necks.”  • 

Steadying  Planes.  It  is  accordingly  necessary  to  adopt  a further 
expedient  to  insure  stability.  This  takes  the  form  of  a system  of 
rigid  planes,  both  vertical  and  horizontal,  located  in  the  axis  of  the 
balloon  and  placed  a considerable  distance  to  the  rear  of  the  center 
of  gravity.  With  this  addition,  the  resemblance  of  the  after  end  of 


DIRIGIBLE  BALLOONS 


21 


the  balloon  to  the  feathering  of  an  arrow  is  apparent,  while  its  pur- 
pose is  similar  to  that  of  the  latter.  For  this  reason,  these  steadying 
planes  have  been  termed  the  empennage,  which  is  the  French  equiva- 
lent of  “arrow  feathering,”  while  its  derivative  empennation  is 
employed  to  describe  the  counteraction  of  this  disturbing  effect. 
In  the  La  France,  which  measured  about  230  feet  in  length  by  40 
feet  in  diameter,  the  area  of  the  planes  required  to  accomplish  this 
was  160  square  feet,  and  the  planes  themselves  were  placed  almost  100 
feet  to  the  rear  of  the  center  of  gravity.  By  referring  to  the 


Fig.  8.  La  Ville  de  Paris  Showing  Balloonets 

illustrations  of  the  various  French  airships,  the  various  developments 
in  the  methods  of  accomplishing  this  will  be  apparent. 

In  the  Lebaudy  balloon,  it  took  the  form  of  planes  attached  .tc 
the  framework  between  the  car  and  the  balloon.  In  La  Patrie 
and  La  Republique,  the  resemblance  to  the  feathered  arrow  was 
completed  by  attaching  four  planes  in  the  form  of  a cross  directly 
to  the  stern  of  the  balloon  itself.  But  as  weight,  no  matter  how  slight, 
is  a disturbing  factor  at  the  end  of  a long  lever,  such  as  is  represented 


22 


DIRIGIBLE  BALLOONS 


by  the  balloon,  Renard  devised  an  improvement  over  these 
methods  by  conceiving  the  use  of  hydrogen  balloonets  as  steadying 
planes.  The  idea  was  first  embodied  in  La  Yille  de  Paris,  Fig.  8, 
in  the  form  of  cylindrical  balloonets,  and  as  conical  balloonets  on 
the  Clement-Bayard.  These  balloonets  communicate  with  the  gas 
chamber  proper  of  the  balloon  and  consequently  exert  a lifting 
pressure  which  compensates  for  their  weight,  so  that  they  no  longer 
have  the  drawback  of  constituting  an  unsymmetrical  supplementary 
load. 

Location  of  Propeller.  The  final  factor  of  importance  in  the 
design  of  the  successful  dirigible  is  the  proper  location  of  the  pro- 
pulsive effort  with  relation  to  the  balloon.  Theoretically,  this 
should  be  applied  to  the  axis  of  the  balloon  itself,  as  the  latter 
represents  the  greater  part  of  the  resistance  offered  to  the  air.  At 
least  one  attempt  to  carry  this  out  in  practice  resulted  disastrously, 
that  of  the  Brazilian  airship  Pax,  while  the  form  adopted  by  Rose, 
in  which  the  propeller  wTas  placed  between  the  twin  balloons  in 
a plane  parallel  with  their  horizontal  axes,  was  not  a success. 
In  theory,  the  balloon  offers  such  a substantial  percentage  of  the 
total  resistance  to  the  air  that  the  area  of  the  car  and  the  rigging 
were  originally  considered  practically  negligible  by  comparison. 
Actually,  however,  this  is  not  the  case.  Calculation  shows  that  in 
the  case  of  any  of  the  typical  French  airships  mentioned,  the  sum 
of  the  surface  of  the  suspending  rigging  alone  is  easily  the  equiv- 
alent of  2 square  meters,  or  about  21  square  feet,  without  taking 
into  consideration  the  numerous  knots,  splices,  pulleys,  and  ropes 
employed  in  the  working  of  the  vessels,  air  tubes  communicating 
with  the  air  balloonets,  and  the  like.  Add  to  this  equivalent  area 
that  of  the  passengers,  the  air  pump,  other  transverse  members 
and  exposed  surfaces,  and  the  total  will  be  found  equivalent  to  a 
quarter  or  even  a third  of  the  transverse  section  of  the  balloon  itself. 

To  insure  the  permanently  horizontal  position  of  the  ship 
under  the  combined  action  of  the  motor  and  the  air  resistance,  a 
position  of  the  propeller  at  a point  about  one-third  of  the  diameter 
of  the  balloon  below  its  horizontal  axis  will  be  necessary.  W ithout 
employing  a rigid  frame  like  that  of  the  Zeppelin  and  the  Pax, 
however,  such  a location  of  the  shaft  is  a difficult  matter  for 
constructional  reasons.  Consequently,  it  has  become  customary  to 


DIRIGIBLE  BALLOONS 


23 


apply  the  driving  effort  to  the  ear  itself,  as  no  other  solution  of 
the  problem  is  apparent.  This  accounts  for  the  tendency  common 
in  the  dirigible  to  “float  high  forward,”  and  this  tilting  becomes 
more  pronounced  in  proportion  to  the  distance  the  car  is  hung 
beneath  the  balloon.  The  term  “deviation”  is  employed  to 
describe  this  tilting  effect  produced  by  the  action  of  the  propeller. 
Conflicting  requirements  are  met  with  in  attempting  to  reduce  this 
by  bringing  the  car  closer  to  the  balloon  as  this  approximation  is 
limited  by  the  danger  of  operating  the  gasoline  motor  too  close 
to  the  huge  volume  of  inflammable  gas.  The  importance  of  this 
factor  may  be  appreciated  from  the  fact  that  if  the  car  were 
placed  too  far  from  the  balloon,  the  propulsive  effect  would  tend  to 
hold  the  latter  at  an  angle  without  advancing  much,  owing  to  the 
vastly  increased  air  resistance  of  the  much  larger  surface  thus 
presented. 

Relations  of  Speed  and  Radius  of  Travel.  The  various  factors 
influencing  the  speed  of  a dirigible  have  already  been  referred  to, 
but  it  will  be  apparent  that  the  radius  of  action  is  of  equally  great 
importance.  It  is  likewise  something  that  has  a very  direct 
bearing  upon  the  speed  and,  in  consequence,  upon  the  design  as  a 
whole.  It  will  be  apparent  that  to  be  of  any  great  value  for 
military  or  other  purposes,  the  dirigible  must  possess  not  only 
sufficient  speed  to  enable  it  to  travel  to  any  point  of  the  compass 
under  ordinarily  prevailing  conditions  of  wind  and  weather  but  also 
to  enable  it  to  remain  in  the  air  for  some  time  and  cover  consider- 
able distance  under  its  own  power. 

Total  Weight  per  Horsepower  Hoar.  As  is  the  case  in  almost 
every  point  in  the  design  of  the  dirigible,  conflicting  conditions 
must  be  reconciled  in  order  to  provide  it  with  a power  plant 
affording  sufficient  speed  with  ample  radius  of  action.  It  has 
already  been  pointed  out  that  power  requirements  increase  as  the 
cube  of  the  speed,  making  a tremendous  addition  necessary  to  the 
amount  of  power  to  obtain  a disproportionately  small  increase 
in  velocity.  In  this  connection  there  is  a phase  of  the  motor 
question  that  has  not  received  the  attention  it  merits  up  to  the 
present  time.  The  struggle  to  reduce  weight  to  the  attainable  mini- 
mum has  made  weight  per  horsepower  apparently  the  paramount 
consideration — a factor  to  which  other  things  could  be  sacrificed. 


24 


DIRIGIBLE  BALLOONS 


And  this  is  quite  as  true  of  aeroplane  motors  as  those  designed  for 
use  in  the  dirigible.  But  it  is  quite  as  important  to  make  the 
machine  go  as  it  is  to  make  it  rise  in  the  air,  so  that  the  question 
of  total  weight  per  horsepower  hour  has  led  to  the  abandonment  of 
extremely  light  engines  requiring  a great  deal  of  fuel. 

Speed  is  quite  as  costly  in  an  airship  as  it  is  in  an  Atlantic 
liner.  To  double  it,  the  motor  power  must  be  multiplied  by  8,  and 
the  machine  must  carry  8 times  as  much  fuel.  But  by  cutting  the 
pPwer  in  half,  the  speed  is  reduced  only  one-fifth.  The  problem 
of  long  voyages  in  the  dirigible  is,  accordingly,  how  to  reconcile 
best  the  minimum  speed  which  will  enable  it  to  make  way  effec- 
tively against  the  prevailing  winds,  with  the  reduction  in  power 
necessary  to  cut  the  fuel  consumption  down  to  a point  that  will 
insure  a long  period  of  running. 

When  the  speed  of  the  dirigible  is  greater  than  that  of  the 
prevailing  wind,  it  may  travel  in  any  direction;  when  it  is  consider- 
ably less,  it  can  travel  only  with  the  wind;  when  it  is  equal  to  the 
speed  of  the  latter,  it  may  travel  at  an  angle  with  the  wind — in  other 
words,  tack,  as  a ship  does,  utilizing  the  pressure  of  the  contrary 
wind  to  force  the  ship  against  it.  But  as  the  air  does  not  offer 
to  the  hull  of  the  airship,  the  same  hold  that  water  does  to  that 
of  the  seagoing  ship,  the  amount  of  leeway  or  drift  in  such  a 
manoeuver  is  excessive.  This  applies  quite  as  much  to  the  aero- 
plane as  it  does  to  the  dirigible. 

FRENCH  DIRIGIBLES 

The  First  Lebaudy.  The  interest  evidenced  by  the  German 
War  Department  in  Zeppelin’s  airship  was  more  than  duplicated 
by  that  aroused  in  French  military  circles  by  the  success  of  the 
Lebaudy  Brothers.  Since  1900  these  two  brothers  had  been  experi- 
menting with  dirigible  balloons.  Their  first  dirigible — built  by  the 
engineer  Juillot — made  thirty  flights,  in  all  but  two  of  which  it 
succeeded  in  returning  to  its  starting  point.  This  machine  was 
somewhat  similar  to  the  later  types  built  by  Santos-Dumont  and 
carried  a 40-horsepower  Daimler  motor.  A speed  of  36  feet  per 
second,  or  about  25  miles  per  hour,  was  obtained.  During  tests 
in  the  summer  of  1904,  the  balloon  was  dashed  against  a tree  and 
almost  entirely  destroyed. 


DIRIGIBLE  BALLOONS 


25 


Lebaudy  1904.  The  next  year  the  “Lebaudy  1904”  appeared. 
This  was  190  feet  long  and  had  a capacity  of  94,000  cubic  feet  of 
gas.  The  air  bag  was  divided  into  three  parts  and  contained 
17,600  cubic  feet  of  air.  It  was  supplied  with  air  from  a fan 
driven  by  the  engine,  and  an  auxiliary  electric  motor  and  storage 
battery  were  carried  to  drive  the  fan  when  the  gas  engine  was  not 
working.  The  storage  battery  was  also  used  to  furnish  electric  lights 
for  the  airship.  A horizontal  sail  of  silk  was  stretched  between  the 
car  and  the  gas  bag,  which  had  an  area  of  something  over  1,000 


Fig.  9.  La  Patrie,  French  War  Dirigible 

square  feet,  and  a sort  of  keel  of  silk  was  stretched  below  it.  A 
horizontal  rudder,  shaped  like  a pigeon’s  tail,  was  used  at  the  rear, 
and  immediately  behind  it  were  two  V-shaped  vertical  rudders. 
A small  vertical  sail  was  carried,  which  could  be  used  to  assist  in 
guiding  the  airship.  The  car  was  16  feet  long  and  was  rigidly  hung 
10  feet  below  the  bag.  It  was  provided  with  an  inverted  pyramid 
of  steel  tubes  meeting  at  an  apex  below  the  car  to  prevent  injury  in 
alighting.  Sixty-three  ascents  were  made  in  1904  with  this  balloon, 
all  of  them  comparatively  successful,  the  longest  being  a journey  of 
60  miles  in  two  hours  and  forty-five  minutes. 


26 


DIRIGIBLE  BALLOONS 


The  next  year  a new  and  larger  balloon  equipped  with  a more 
powerful  motor  was  used.  Many  flights  were  made  in  tests  for  the 
French  War  Department. 

La  Patrie.  La  Patrie  was  then  built  for  the  French  govern- 
ment by  the  Lebaudy  Brothers  and  was  of  the  same  design  as  their 
earlier  airships.  In  speed  it  was  nearly  equal  to  Zeppelin’s,  and  its 
dirigibility  was  nearly  perfect.  Fig.  9 shows  a view  of  this  airship 
in  flight. 

It  was  200  feet  long,  and  the  70-horsepower  engine  drove  two 
propellers.  It  could  carry  seven  people  and  one-half  ton  of  ballast. 
It  carried  four  people  at  a speed  of  30  miles  per  hour.  On  its  last 
trip  it  covered  175  miles  in  seven  hours.  A few  days  afterward,  a 
heavy  wind  tore  it  away  from  its  moorings  and  it  was  blown  out 
to  sea  and  lost. 

La  Republique  and  Le  Jaune.  Two  more  airships  of  the  same 
type,  La  Republique  and  Le  Jaune,  followed  this.  These  were 
tried  by  the  French  government,  in  1908,  and  both  proved  success- 
ful. La  Republique  is  illustrated  in  Fig.  10.  The  shape  and  equip- 
ment of  the  car  are  shown  in  Fig.  1 1 . The  automobile  type  of 
radiator  may  be  seen  attached  to  the  side  of  the  car.  During  a 
flight  in  the  fall  of  1909,  a propeller  blade  broke  and  was  thrown 
clear  through  the  balloon  envelope,  causing  the  balloon  to  fall  from 
a height  of  500  feet.  The  four  officers  who  formed  the  crew  of  the 
dirigible  were  killed  instantly. 

Clement=Bayard  II.  The  numerous  factors  that  must  be  con- 
sidered in  the  design  of  a successful  dirigible  balloon  as  well  as  the 
many  conflicting  conditions  that  must  be  reconciled  have  already 
been  referred  to  in  detail.  How  these  are  carried  out  in  practice 
may  best  be  made  clear  by  a description  of  what  may  be  con- 
sidered as  an  advanced  type  of  dirigible,  the  Clement-Bayard  II, 
Fig.  12,  of  French  design,  and  the  most  successful  of  the  French 
military  air  fleet.  Its  predecessor,  the  Clement-Bayard  I,  Fig.  13, 
made  thirty  voyages,  some  of  them  of  considerable  distances, 
without  suffering  any  damage,  but  a study  of  its  shortcomings  led 
to  their  elimination  in  the  following  model. 

The  pisciform  shape  of  the  first  Clement-Bayard  was  retained 
but  given  more  taper,  the  dimensions  being  248.6  feet  overall  by 
42.9  greatest  diameter,  this  being  but  a short  distance  back  of  the 


DIRIGIBLE  BALLOONS 


27 


Fig.  10.  La  Republique,  French  War  Dirigible 


Fig.  11.  Car  of  La  Republique 


28 


DIRIGIBLE  BALLOONS 


bow.  This  gives  it  a ratio  of  length  to  diameter  of  5.76.  The  gas 
balloonet  stabilizers  were  eliminated  altogether,  Fig.  12.  The  total 
gas  capacity  is  approximately  80,000  cubic  feet.  Like  all  French 
dirigibles  it  is  of  the  true  flexible  type,  the  only  rigid  construction 
being  that  of  the  framework  of  the  car  itself.  To  the  latter  are 
attached  all  rudders  and  stabilizing  devices,  instead  of  making  them 


Fig.  12.  Clement-Bayard  II,  French  Dirigible 

a part  of  the  envelope  as  formerly.  The  latter  is  made  of  conti- 
nental rubber  cloth. 

Light  steel  and  aluminum  tubing  are  employed  in  the  construc- 
tion of  the  frame  supplemented  by  numerous  piano-wire  stays. 
This  frame  extends  almost  the  entire  length  of  the  envelope  and 
carries  at  its  rear  end  a cellular,  or  box-kite,  type  of  stabilizing 
rudder,  instead  of  the  former  gas  balloonets  employed  on  the 
Clement-Bayard  I,  Fig.  13.  This  cellular  rudder  is  in  two  parts, 


DIRIGIBLE  BALLOONS 


29 


consisting  of  two  units  of  four  cells  each,  the  two  groups  being 
joined  at  the  top,  with  a space  between  them.  In  addition  to 
acting  as  a stabilizer,  this  is  also  the  direction  rudder,  its  leverage 
being  increased  by  making  the  end  planes  somewhat  larger  than 
the  partitions  of  the  cells.  Between  the  cellular  stabilizing  rudder 
and  the  envelope  is  placed  the  horizontal  rudder  for  ascending  or 
descending.  In  the  illustration  this  appears  to  be  a flag,  but  it 
is  in  reality  a long  rectangular  plane,  which  may  be  tilted  on  its 
longitudinal  axis,  the  latter  being  at  right  angles  to  that  of  the 


Fig.  13.  Clement-Bayard  I 

balloon.  There  are  two  air  balloonets  of  about  one-third  the  total 
capacity  of  the  balloon  itself,  and  they  are  designed  to  be  inflated 
by  large  aluminum  centrifugal  blowers  driven  from  the  main 
engines  themselves. 

There  are  two  motors,  each  of  125  horsepower,  both  being  of 
the  same  conventional  design,  i.e.,  four  cylinder  four  cycle  vertical 
water  cooled.  In  fact,  they  are  merely  light  automobile  motors. 
The  cylinders  have  separate  copper  water  jackets  and  the  motors 
themselves  are  muffled,  which  is  a departure  from  the  usual  custom. 


30 


DIRIGIBLE  BALLOONS 


Each  drives  a separate  propeller  carried  on  top  of  the  main  frame 
through  bevel  gearing. 

The  Clement-Bayard  II  made  itself  famous  by  its  rapid  and 
successful  flight  from  the  suburbs  of  Paris  across  the  Channel  to 
London,  in  October,  1910. 

Astra=Torres.  In  reviewing  the  specifications  of  any  of  the 
big  dirigibles,  the  observer  cannot  fail  to  be  struck  by  the  excessive 
amount  of  power  necessary  to  drive  them  at  speeds  which  are 
lower  than  the  minimum,  or  landing  speeds,  of  many  aeroplanes. 
When  a speed  of  45  miles  per  hour  was  first  reached  by  a dirigible, 
it  was  acclaimed  as  a great  feat.  But  this  comparatively  moderate 
rate  of  travel  was  surpassed  only  by  increasing  the  number  of 
motors  and  their  horsepower  until  the  fuel  consumption  became 
exceedingly  high.  This  necessitated  the  carrying  of  a great  weight 
of  fuel  and  cut  down  correspondingly  the  useful  load  that  the 
dirigible  was  capable  of  lifting  as  well  as  restricted  its  radius  of 

flight  at  full  speed.  Lentil  aero- 
dynamic research  had  demon- 
strated the  contrary,  the  necessity 
for  such  a tremendous  amount  of 
power  was  considered  necessary  to 
overcome  the  head  resistance  of  the 
balloon  itself.  Research  brought 
out  in  a striking  manner  how  great 
a proportion  of  the  total  head 
resistance  of  an  aeroplane  was  due 
to  the  struts  and  bracing  wires. 
In  the  construction  of  the  different 
types  of  airships  illustrated,  it  will 
be  noted  that  the  gear  provided 
for  suspending  the  car  or  cars  below 
the  balloon  requires  a great  number 
of  cables.  Later  developments  showed  that  by  eliminating  the 
great  amount  of  head  resistance  caused  by  these  numerous  surfaces, 
the  speed  of  a dirigible  could  be  increased  by  over  50  per  cent  with 
the  same  amount  of  power. 

Improved  Suspension.  The  shortcoming  of  the  dirigible  with 
reference  to  suspension  was  realized  more  than  ten  years  previous 


Fig.  14.  Section  of  Astra-Torres,  Illustra- 
ting Method  of  Suspension.  CB,  Brac- 
ing of  Heavy  Fabric  Bands;  SR  and  A, 
Suspension  Ropes  and  Cable  Passing 
through  Envelope;  S,  Expansion  Sleeve 
in  Envelope;  CC',  Ropes  to  Sides  of 
Car;  E,  Envelope 


DIRIGIBLE  BALLOONS 


31 


by  a Spaniard — Torres — but  owing  to  lack  of  financial  support,  he 
was  unable  to  put  his  idea  into  execution.  The  principle  he  evolved 
is  made  clear  by  Fig.  14,  which  gives  a section  of  an  Astra-Torres 
dirigible  illustrating  the  method  of  suspension.  Instead  of  the 
ropes  SR  used  to  suspend  the  car  being  attached  to  bands  passing 
around  the  envelope,  these  reinforcing  bands  CB  and  also  the  ropes 
fastened  to  them  are  placed  inside  the  envelope,  thus  eliminating 
head  resistance  from  those  sources. 

Performance.  Failing  to  obtain  any  encouragement  in  Spain, 
Torres  finally  succeeded  in  interesting  the  French  Astra  Company, 
which  built  a vedette,  or  scouting  airship,  of  a little  over  50,000 
cubic  feet  capacity.  It  was  pitted  against  the  Colonel  Renard,  at 
that  time  the  leading  unit  in  the  French  aerial  navy  and  the 
fastest  airship  in  commission.  The  small  Torres  dirigible  so  com- 
pletely outclassed  its  huge  competitor  that  another  of  close  to 
300,000  cubic  feet  capacity  was  built  and  tried  against  the  Parseval 
with  similar  results.  An  Astra-Torres  dirigible  built  for  the 
British  government  showed  a speed  in  excess  of  50  miles  per  hour. 
This  particular  dirigible  has  been  at  the  front  in  France  almost 
since  the  outbreak  of  hostilities  and  has  rendered  considerable 
valuable  service.  Its  success  led  the  French  Government  to  order 
a huge  replica  of  it,  having  a capacity  of  over  800,000  cubic  feet 
and  with  motors  developing  1,000  horsepower,  which  would  give 
it  an  indicated  speed  of  60  miles  per  hour.  So  confident  were  its 
builders  of  attaining  or  even  exceeding  this,  that  an  order  for  a 
second  and  even  larger  airship  of  the  Astra-Torres  design  was 
placed  before  the  first  one  was  finished.  This  is  also  fitted  with 
motors  aggregating  1,000  horsepower  and  displaces  38  tons,  making 
it  larger  than  any  Zeppelin  that  had  been  constructed  up  to  the 
time  it  was  built.  As  its  construction  and  trials  were  undertaken 
during  the  war,  no  details  have  been  published,  but  it  is  said  on 
good  authority  that  its  speed  exceeds  60  miles  per  hour,  so  that  it 
is  faster  than  any  of  the  German  dirigibles. 

Construction.  LAilike  the  German  dirigibles,  the  larger  types 
of  which  have  been  characterized  by  a rigid  frame,  the  Astra-Torres 
is  a flexible  airship  and,  owing  to  its  method  of  suspension,  its 
external  appearance  is  decidedly  unconventional,  since  the  envelope 
instead  of  being  of  the  usual  cigar  shape  is  more  like  a triangular 


32 


DIRIGIBLE  BALLOONS 


bundle  of  three  cigars  with  the  third  one  on  top.  At  the  point 
where  the  three  envelopes  join,  as  shown  in  section,  Fig.  14,  heavy 
cloth  bands  CB  are  stretched  across  the  arcs,  forming  a chord 
across  each  arc,  the  three  chords  comprising  an  inverted  triangle. 
The  suspension  ropes  SR  are  attached  to  the  opposite  ends  of  the 
base  of  this  inverted  triangle  and  converge  in  straight  lines  down- 
ward through  the  gas  space,  so  that  the  air  resistance  offered  by 
the  ropes  is  practically  eliminated  since  only  a very  small  part  of 
the  suspension  system  appears  outside  the  envelope.  This  external 
part  consists  of  vertical  cables  A attached  to  the  collecting  rings 
of  the  bracing  system  and  extending  downward  through  special 
accordion  sleeves  S which  permit  the  free  play  necessary  at  the 
points  where  they  pass  through  the  outer  wall  of  the  envelope. 
These  sleeves  also  have  another  function — that  of  permitting  the 
escape  of  gas  under  the  pressure  of  expansion.  A short  distance 
below  the  envelope  E each  of  these  cables  splits  into  two  parts  C 
and  C'  attached  to  opposite  sides  of  the  car. 

The  British  airship  mentioned  is  provided  with  but  one  car, 
but  the  larger  French  ships  have  two  placed  tandem,  each  of  which 
carries  a 500-horsepower  motor  driving  two  two-bladed  propellers 
of  large  diameter.  While  the  form  of  envelope  made  necessary  by 
this  construction  increases  the  frictional  resistance,  this  is  negligible 
in  comparison  with  the  great  saving  in  power  effected  by  the  method 
of  suspension,  not  to  mention  the  greater  simplicity  of  construction. 

GERMAN  DIRIGIBLES 

Early  Zeppelin  Airships.  At  the  same  time  that  Santos-Dumont 
was  carrying  on  his  hazardous  experiments,  the  problem  was  being 
attacked  along  slightly  different  lines  by  Count  Zeppelin. 

It  will  be  remembered  that  Dumont  experienced  much  trouble 
on  account  of  the  envelope  of  his  balloon  being  too  flexible,  causing 
it  to  crumple  in  the  middle  and  to  become  distorted  in  shape  from 
the  pressure  of  the  air.  His  efforts  to  overcome  this  by  the  employ- 
ment of  air  bags  did  not  meet  with  great  success,  even  in  his  later 
types. 

Construction.  Zeppelin  employed  a very  rigid  construction. 
Flis  first  balloon,  which  was  built  in  1S9S,  was  the  largest  which 
had  ever  been  made.  It  is  illustrated  in  Fig.  15,  which  shows  his 


DIRIGIBLE  BALLOONS 


33 


first  design  slightly  improved.  It  was  about  40  feet  in  diameter 
and  420  feet  long — an  air  craft  as  large  as  many  an  ocean  vessel. 
The  envelope  consisted  of  two  distinct  bags,  an  outer  and  an  inner 
one,  with  an  air  space  between.  The  air  space  between  the  inner 
and  outer  envelopes  acted  as  a heat  insulator  and  prevented  the 
gas  within  from  being  affected  by  rapid  changes  of  temperature. 
The  inner  bag  contained  the  gas,  and 'the  outer  one  served  as  a 
protective  covering.  In  the  construction  of  this  outer  bag  lies  the 
novelty  of  Zepplin’s  design.  A rigid  framework  of  strongly  braced 
aluminum  rings  was  provided  and  this  was  covered  with  linen  and 
silk  which  had  been  specially  treated  to  prevent  leakage  of  gas. 


Fig.  15.  Zeppelin  Dirigible  Rising  from  Lake  Constance 

The  inner  envelope  consisted  of  seventeen  gas-tight  compartments 
which  could  be  filled  or  emptied  separately.  In  the  event  of  the 
puncture  of  one  of  them,  the  balloon  would  remain  afloat.  An 
aluminum  keel  was  provided  to  further  increase  the  rigidity.  A 
sliding  weight  could  be  moved  backward  or  forward  along  the  keel 
and  cause  the  nose  of  the  airship  to  point  upward  or  downward  as 
desired.  This  would  make  the  craft  move  upward  or  downward 
without  throwing  out  ballast  or  losing  gas.  Lender  each  end  of  the 
balloon  a light  aluminum  car  was  rigidly  fastened  and  in  each  -was 
a 16-horsepower  Daimler  gasoline  engine.  The  two  engines  could 
be  worked  either  independently  of  each  other  or  together.  Each 
engine  drove  a vertical  and  horizontal  propeller.  The  propellers 


34 


DIRIGIBLE  BALLOONS 


each  had  four  aluminum  blades.  As  will  be  seen  from  Fig.  15,  the 
ears  were  too  far  apart  for  ordinary  means  of  communication  and  so 
speaking  tubes,  electric  bells,  and  an  electric  telegraph  system  were 
installed. 

First  Trials.  Very  little  was  known  as  to  the  effects  of  alight- 
ing on  the  ground  with  such  a rigid  affair  as  this  vessel,  therefore 
the  cars  were  made  like  boats  so  that  the  airship  could  alight  and 
float  on  the  water.  The  first  trials  were  made  over  Lake  Constance 
in  July,  1900.  The  mammoth  craft  was  housed  in  a huge  floating 
shed,  and  the  vessel  emerged  from  it  with  the  gas  bag  floating 
above  and  the  two  cars  touching  the  water.  She  rose  easily  from 
the  water,  and  then  began  a series  of  mishaps  such  as  usually  fall 
to  the  lot  of  experimenters.  The  upper  cross  stay  proved  too 
weak  for  the  long  body  of  the  balloon  and  bent  upward  about 
10  inches  during  the  flight.  This  prevented  the  propeller  shafts 
from  working  properly.  Then  the  winch  which  worked  the  sliding 
weight  was  broken  and,  finally,  the  steering  ropes  to  the  rudders 
became  entangled.  In  spite  of  all  this,  a speed  of  13  feet  per 
second,  or  about  9 miles  per  hour,  was  obtained.  These  breakages 
made  it  necessary  to  descend  to  the  lake  for  repairs  and  in  alight- 
ing the  framework  was  further  damaged  by  running  into  a pile 
in  the  lake.  The  airship  was  repaired  and  another  flight  was  made 
later  in  the  year,  during  which  a speed  of  30  feet  per  second,  or 
20  miles  per  hour,  was  obtained. 

Second  Airship.  Zeppelin  had  sunk  his  own  private  fortune 
and  that  of  his  supporters  in  his  first  venture,  and  it  was  not  till 
five  years  later  that  he  succeeded  in  raising . enough  money  to 
construct  a second  airship.  No  radical  changes  in  construction 
were  made  in  the  new  model,  but  there  were  slight  improvements 
made  in  all  its  details.  The  balloon  was  about  8 feet  shorter  than 
the  original  and  the  propellers  were  enlarged.  Three  vertical  rud- 
ders were  placed  in  front  and  three  behind  the  balloon,  and  below 
the  end  of  the  craft  horizontal  rudders  were  installed  to  assist  in 
steering  upward  or  downward.  The  steering  was  taken  care  of 
from  the  front  car. 

The  most  important  change  was  made  possible  by  the  improve- 
ment in  gasoline  engines  during  the  preceding  five  years.  V here, 
in  the  earlier  model,  he  had  two  16-horsepower  engines,  he  now 


DIRIGIBLE  BALLOONS 


35 


used  an  85-horsepower  engine  in  each  ear,  with  practically  the  same 
weight.  In  fact,  the  total  weight  of  the  vessel  was  only  9 tons, 
while  his  first  airship  weighed  10  tons. 

His  new  craft  made  many  successful  flights.  One  was  made 
at  the  rate  of  38  miles  per  hour  and  continued  for  seven  hours, 
covering  a total  distance  of  266  miles. 

Later  Zeppelins.  The  later  Zeppelins  embody  no  remarkable 
changes  in  design,  the  principal  alteration  being  in  size.  One  of 
these  is  illustrated  in  Fig.  16.  In  this  the  gas  bag  was  increased 


to  446  feet  in  length  and  it  held  over  460,000  cubic  feet  of  gas. 
This  gave  it  a total  lifting  power  of  16  tons.  With  this,  Zeppelin 
made  a voyage  of  over  375  miles.  He  was  in  the  air  for  twenty 
hours  on  this  trip  and  carried  eleven  passengers  with  him. 

In  August,  1908,  the  Zeppelin  left  its  great  iron  house  at  Fried- 
richshafen  and  sailed  in  a great  circle  over  Lake  Constance.  The 
day  after  it  started,  however,  it  was  destroyed  by  a storm,  and  sudden 
destruction  from  one  cause  or  another  has  ended  the  existence  of 
practically  every  one  of  the  Zeppelins  built  since,  usually  after  a 
very  brief  period  of  service. 


Fig.  16.  Zeppelin  Airship  in  Flight 


36 


DIRIGIBLE  BALLOONS 


Shape  and  Framing.  In  the  early  days  of  dirigible  design 
the  data  upon  which  the  shape  and  proportions  of  the  envelope 
were  based  were  purely  empirical.  Schwartz,  Germany’s  pioneer 
in  this  field,  adopted  the  projectile  as  representing  the  form  offer- 
ing the  least  air  resistance  and  accordingly  designed  his  envelope 
with  a sharply  pointed  bow  and  a rounded-off  stern,  giving  it 
a length  four  times  its  diameter.  Zeppelin  did  not  agree  with 
these  conclusions  and  adopted  a pencil  form,  rounded  at  the  nose 
and  tapering  to  a sharp  point  at  the  stern,  making  the  length 
nine  to  ten  times  the  diameter.  Subsequent  research  work  in  the 
aerodynamic  laboratory  has  demonstrated  that  the  most  efficient 
form  for  air  penetration  is  one  having  a length  six  times  its  maxi- 
mum diameter  with  the  latter  situated  at  a point  four-tenths  of 
the  total  length  from  the  bow.  It  has  likewise  been  proved  that 
an  ellipse  is  more  efficient  than  either  the  projectile  or  pencil  form 
and  that  tapering  to  a sharp  point  at  the  stern  offers  no  particular 
advantage.  As  a result,  the  most  approved  form  resembles  the 
shape  of  a perfecto  cigar,  the  nose  being  somewhat  blunter  than 
the  after  end.  This  form  is  likewise  that  of  the  swiftest-swjmming 
fishes  and  has  been  shown  to  have  the  least  head  resistance  as 
well  as  the  minimum  skin  friction;  it  results  in  a section  to  which 
the  term  stream-line  has  been  applied,  and  it  is  now  employed  on 
all  exposed  non-supporting  surfaces  on  aeroplanes,  such  as  the  struts 
and  even  the  bracing  cables.  Laboratory  research  has  demon- 
strated that  it  is  worth  while  to  reduce  the  head  resistance  of  even 
such  apparently  negligible  surfaces  as  those  presented  by  these  wires 
and  cables  and,  therefore,  they  are  stream-lined  by  attaching  recessed 
triangular  strips  of  wood  to  their  forward  sides. 

Framing  Details.  Despite  this,  the  builders  of  the  Zeppelins 
have  adhered  to  the  original  pencil  shape  with  but  slight  modifi- 
cations at  the  bow  and  stern,  probably  because  that  shape  is 
much  easier  to  build  and  assemble  from  standard  girders.  The 
form  of  girder  employed  is  shown  in  Fig.  17,  while  the  complete 
assembly  of  the  frame  is  illustrated  in  Fig.  18.  The  girders  form 
the  longerons,  or  longitudinal  beams,  running  the  entire  length  of 
the  rigid  frame  and  supported  at  equidistant  points  by  ring 
members  built  of  similar  girder  sections.  The  fourth  ring  from  the 
nose  and  each  alternate  ring  after  that  are  further  braced  by  being 


DIRIGIBLE  BALLOONS 


37 


trussed  to  the  longitudinal  beams  around  their  entire  circumferences, 
as  shown  in  Fig.  18.  The  larger  V-shaped  truss  at  the  bottom 
forms  the  gangway,  which  is  now  placed  inside  the  envelope 
instead  of  being  suspended  beneath  it,  as  formerly.  This  is  done 
to  eliminate  the  head  resistance  set  up  by  the  additional  surface 


Fig.  17.  Trellis  Type  of  Aluminum  Girder  used  in  Longi- 
tudinals of  Zeppelin  Frame 


thus  exposed.  In  the  first  instance  in  which  this  gangway  was 
incorporated  in  the  envelope,  no  provision  was  made  for  ventila- 
tion, and  the  ship  was  wrecked  by  a gas  explosion.  Regardless  of 
how  tight  the  fabric  is  made,  gas  is  always  oozing  out  through  it 
to  a greater  or  less  extent.  This  fact  is  now  met  by  providing 
ventilating  shafts  leading  from  the  gangway  to  the  upper  surface 


Pig.  18.  Aluminum  Frame  Construction  of  Zeppelin  Hull 


of  the  envelope.  Additional  shafts  through  the  envelope  lead  to 
gun  platforms,  forward,  amidships,  and  aft,  and  are  reached  by 
aluminum  ladders. 

Framing  of  Schutte-Lanz  Type.  It  has  become  customary  to 
refer  to  all  large  German  airships  as  Zeppelins,  but  many  of  those 
used  during  the  past  three  years  have  been  of  the  Schutte-Lanz 


38 


DIRIGIBLE  BALLOONS 


build,  which  is  also  a rigid  frame  type  of  dirigible  but  has  been 
designed  with  a view  of  overcoming  some  of  the  disadvantages  of 
the  aluminum  frame  construction  encountered  in  the  use  of  the 
Zeppelin.  The  length  and  diameter  of  the  latter  airships  are  such 
that,  no  matter  how  rigidly  the  framing  is  assembled,  there  is  more 
or  less  sag.  When  the  sag  exceeds  a certain  amount,  the  frame 
is  apt  to  buckle  at  the  point  where  it  occurs,  involving  expensive 
repairs  or  wrecking  the  airship  altogether.  To  overcome  this 
difficulty,  the  Schutte-Lanz  type  employs  a rigid  frame  of  flexible 
material,  namely,  laminated  wood  in  strip  form,  held  together  at 
joints  and  crossings  by  aluminum  fittings  and  braced  inside  by 
cables.  As  shown  by  Fig.  19,  no  rigid  longitudinal  beams  are 
employed,  the  only  girders  used  being  rings,  to  which  a network 
built  of  the  wood  strips  is  attached.  Starting  at  the  nose,  each 
continuous  strip  follows  an  open  spiral  path  such  as  would  be 


Fig.  19.  Schutte-Lanz  Type  of  Frame  Construction  of  Laminated  Wood  with 
Aluminum  Fittings 


traced  in  the  air  by  a screw  of  very  large  pitch,  in  fact,  approxi- 
mating the  rifling  of  a gun  barrel.  It  will  also  be  noted  from  the 
illustration  that  the  form  of  the  Schutte-Lanz  airship  is  the  cigar- 
shape,  which  laboratory  research  has  shown  to  be  the  most  efficient. 

The  use  of  wood  in  conjunction  with  the  spiral  construction  of 
the  supporting  members  of  the  framing  affords  the  maximum  degree 
of  flexibility,  since  the  displacement  of  any  of  these  members  under 
stresses  of  either  tension  or  compression  would  have  to  be  very 
great  to  cause  damage  to  the  frame  as  a whole.  The  frame  not 
being  rigid,  strictly  speaking,  either  as  units  or  as  a complete 
assembly,  stress  at  any  particular  point  would  simply  cause  all  the 
members  near  that  point  to  give  in  the  direction  of  the  strain, 
and  the  rest  of  the  frame  would  accommodate  itself  to  their  change 
of  position  by  either  elongating  or  shortening  slightly.  In  addition 
to  these  advantages,  the  Schutte-Lanz  type  of  construction  is  said 


DIRIGIBLE  BALLOONS 


39 


to  be  lighter  than  the  Zeppelin  for  an  airship  of  the  same  load- 
carrying  capacity. 

Power  Plant.  Compared  with  their  successors  of  war  times, 
the  early  Zeppelins  were  mere  pigmies  where  power  is  concerned. 
Many  of  these  pioneers  were  driven  by  less  than  100  horsepower 
all  told,  whereas  in  the  later  types  no  single  motor  unit  as  small  as 
this  total  has  been  employed.  The  motors  used  most  largely 
have  been  the  160-horsepower  Mercedes  and  the  200-horsepower 
Maybach,  both  of  which  are  described  in  detail  under  the  title 
“Aviation  Motors.”  From  five  to  ten  of  these  units  have  been 
used  on  a single  ship,  giving  an  aggregate  in  some  of  the  latest 
types  of  close  to  2,000  horsepower.  Power  has  been  applied 
through  five  or  six  propellers  to  limit  their  diameter  and  to  guard 
against  the  breakdown  of  any  one  of  the  units  putting  the  power 
plant  out  of  commission  as  a whole.  To  distribute  the  weight  of 
the  engines  equally  and  to  insure  each  propeller  a position  in  which 
it  can  work  in  undisturbed  air,  the  engines  have  been  placed  at 
widely  separated  points  on  the  airship  and  in  different  planes  so 
that  no  two  are  coaxial.  The  main  engine  room  is  usually  located 
in  a cabin  just  back  of  the  operating  bridge  and  wireless  room, 
while  the  remaining  motors  are  suspended  in  independent  gondolas 
at  different  points  along  the  sides.  Where  more  than  1,000  horse- 
power has  been  used,  each  of  these  gondolas'  has  been  fitted  with 
two  motors  placed  side  by  side  and  so  coupled  that  either  one  or 
both  may  be  employed  to  drive  the  single  propeller  carried  by  the 
propelling  car.  All  the  more  recent  propellers  have  been  of  the  two- 
bladed  type. 

Control  Surfaces.  The  numerous  expedients  formerly  resorted 
to  by  various  designers  in  providing  for  stabilizing,  steering,  and 
elevating  surfaces  have  been  abandoned  for  forms  that  are  practi- 
cally a duplication  of  aeroplane  practice.  Experience  demonstrated 
that  the  different  types  of  multiplane  rudders,  elevators,  and  stabil- 
izing surfaces  employed  in  earlier  days  not  only  offered  no  operating 
advantages  but  were  actually  detrimental,  in  that  they  increased 
the  head  resistance  unnecessarily.  Moreover,  their  complication 
meant  increased  weight  and  weaker  construction.  They  have 
accordingly  been  displaced  by  monoplane  surfaces  which  are  of 
exactly  the  same  type  of  construction  as  those  used  on  the  aero- 


40 


DIRIGIBLE  BALLOONS 


plane  and  the  location  and  proportions  of  which  are  very  evi- 
dently based  on  aeroplane  practice.  Both  the  horizontal  and 
vertical  stabilizers  are  of  approximately  triangular  form  and  have 
the  steering  and  elevating  surfaces  hinged  to  them  at  their  after 
ends,  so  that,  except  for  the  pointed  extremity  of  the  envelope 
which  extends  beyond  them,  the  tail  unit  of  the  later  Zeppelins  is 
practically  the  same  as  the  empennage  of  an  aeroplane.  The 
horizontal  surfaces  are  apparently  depended  on  entirely  to  effect 
the  ascent  and  descent,  there  being  no  evidence  of  swiveling  pro- 
pellers by  means  of  which  the  power  of  the  engines  could  be 
employed  to  draw  the  airship  up  or  down.  The  great  weight  of 
ballast  carried  is,  of  course,  in  the  form  of  water,  but  this  is 
discarded  in  order  to  ascend  only  when  the  power  of  the  engines 
exerted  against  the  elevating  planes  is  no  longer  capable  of  keeping 
the  airship  at  the  altitude  desired.  In  the  low  temperatures 
encountered  in  night  flights,  however,  the  contraction  of  the  hydro- 
gen gas  is  so  great  that  the  crew  has  found  it  necessary  to  reduce 
the  weight  by  discarding  not  only  every  pound  of  ballast  but,  as 
far  as  possible,  everything  portable.  Despite  this,  several  airships 
have  fallen  when  their  fuel  supply  was  exhausted,  one  coming  to  the 
ground  in  Scotland,  two  dropping  into  the  North  Sea,  and  three 
or  four  falling  in  France. 

Operating  Controls.  All  the  operating  controls  are  centered  at 
the  navigating  bridge,  which  is  inclosed  to  form  the  commander’s 
cabin.  By  means  of  push  buttons,  switches,  levers,  and  wheels 
every  operating  function  required  is  set  into  motion  from  this 
central  point.  Whether  auxiliary  motors  are  carried  for  the  pur- 
pose of  pumping  air  into  the  balloonets  or  this  is  one  of  the  duties 
of  the  main  engine  just  back  of  the  wireless  room  does  not  appear, 
but  with  the  aid  of  a push  button  board  the  amount  of  air  in  any 
of  the  balloonets  may  be  increased  or  decreased  at  will.  There  is 
a control  button  for  each  operation,  or  two  for  each  balloonet, 
which  fact  necessitates  a rather  forbidding  looking  board,  since  the 
more  recent  Zeppelins  have  seventeen  to  nineteen  gas  bags  within 
each  of  which  is  incorporated  an  air  balloonet. 

The  amount  of  fuel  supplied  to  any  one  of  the  motor  units 
can  likewise  be  controlled  from  a central  board,  and  this  is  also 
true  of  the  ballast  release  apparatus,  so  that  water  can  be  emptied 


DIRIGIBLE  BALLOONS 


41 


from  any  one  of  the  ballast  tanks  at  will,  thus  facilitating  ascent 
or  descent  by  lightening  one  end  or  the  other.  Elevating  and 
steering  surfaces  are  operated  by  small  hand-steering  wheels  with 
cables  passing  around  their  drums,  a member  of  the  crew  being 
stationed  at  each  of  these  controlling  wheels.  Owing  to  the  num- 
ber of  motors  used,  the  instrument  board  is  the  most  formidable 
appearing  piece  of  apparatus  on  the  bridge,  since  there  is  a revo- 
lution counter  for  each  power  unit  in  addition  to  the  numerous 
other  instruments  required.  Some  of  these  instruments  are  the 
aneroid  barometer  for  indicating  the  altitude,  transverse  and 
longitudinal  clinometers  to  show  the  amount  of  heel  and  the  angle 
at  which  the  airship  is  traveling  with  relation  to  the  horizontal, 
the  anemometer,  or  air-speed  indicator,  manometers,  or  pressure 
gauges,  for  each  one  of  the  gas  bags,  fuel  and  ballast  supply 
gauges,  drift  indicators,  electric  bomb  releasers,  mileage  recorders, 
and  the  like.  In  addition  to  these,  there  are  a large  chart  and  a 
compass,  so  the  navigating  bridge  of  a Zeppelin  combines  in  small 
space  all  the  instruments  to  be  found  in  the  engine  room  and  on 
the  bridge  of  an  ocean  liner  besides  several  which  the  latter  does 
not  require.  That  the  proper  coordination  of  all  the  functions  men- 
tioned is  an  exceedingly  difficult  task  for  one  man  seems  evident 
from  the  numerous  Zeppelins  that  have  apparently  wrecked  them- 
selves. 

Crew  Carried.  In  the  various  Zeppelins  that  have  been  cap- 
tured or  shot  down  by  the  British  or  French,  the  personnel  has 
varied  from  fifteen  to  thirty  men  but  in  the  majority  of  instances 
has  not  exceeded  twenty.  The  positions  and  duties  are  about  as 
follows:  The  commander,  lieutenant-commander,  and  chief  engi- 

neer, and  possibly  a navigating  officer  are  stationed  at  the  bridge. 
Two  or  three  of  the  crew  are  also  stationed  there  to  work  the 
manually  operated  controls.  In  the  cabin  just  back  of  the  bridge 
are  two  wireless  operators  and  one  or  two  engine  attendants  for 
the  motors  in  the  engine  room  behind  the  wireless  room.  A 
similar  number  of  engine  attendants  are  stationed  in  the  after 
engine  room  and  there  is  at  least  one  attendant  for  each  of  the 
other  motor  units.  One  man  is  stationed  at  each  machine  gun,  of 
which  there  are  three  to  five  on  the  “roof”  and  two  in  each  car, 
and  at  least  as  many  bombers  are  needed  to  load  the  “droppers.” 


42 


DIRIGIBLE  BALLOONS 


As  a reserve  there  are  usually  an  additional  gun  pointer  for  each 
gun  and  an  extra  engine  attendant,  since  to  run  continuously  most 
of  the  crew  would  have  to  stand  watch  and  watch  as  in  marine 
practice.  The  sleeping  accommodations  consist  of  canvas  hammocks 
slung  in  the  gangway. 

Explosives  Carried.  In  addition  to  a liberal  supply  of  ammu- 
nition for  the  machine  guns,  a large  weight  of  bombs  is  carried, 
though  the  quantity  as  well  as  the  size  of  the  bombs  themselves 
has  been  exaggerated  in  the  same  or  even  greater  ratio  than  that 
which  has  proved  characteristic  of  the  German  military  press- 
agency  service.  The  bombs  are  carried  suspended  in  racks  amid- 
ships, and  the  bomb  droppers  are  also  located  at  that  part  of  the 
ship  so  that  the  release  of  the  bombs  will  not  upset  the  longitudinal 
equilibrium  of  the  craft.  The  bomb-dropping  apparatus  is  con- 
trolled electrically  from  the  navigating  bridge  but  may  also  be 
operated  by  hand  from  the  same  point.  It  has  been  reported  by 
the  Germans  that  their  latest  types  of  Zeppelins  are  capable  of 
dropping  bombs  weighing  1 ton  each.  In  view  of  the  effect  that 
the  sudden  release  of  a weight  of  1 ton  would  have  on  the  airship 
itself,  this  is  manifestly  very  much  of  an  exaggeration.  Zeppelin 
bombs  that  have  failed  to  explode  have  never  exceeded  200  to  300 
pounds  and  many  of  those  employed  are  doubtless  still  lighter. 
So  far  as  the  total  amount  carried  is  concerned,  many  of  the  later 
airships  doubtless  are  capable  of  transporting  2 to  3 tons  and  still 
carrying  sufficient  fuel,  though  adverse  conditions  would  prevent 
their  return,  as  has  frequently  happened. 

BRITISH  WAR  DIRIGIBLES 

Adoption  of  Small  Type.  German  designers  have  continued 
to  pin  their  faith  blindly  to  the  huge  rigid  type,  despite  the  fact 
that  prior  to  the  war  almost  a dozen  of  these  costly  machines  met 
with  disaster  as  fast  as  they  could  be  turned  out.  Since  the 
war  started,  their  destruction  has  kept  pace  pretty  closely  with 
their  building  without  their  accomplishing  anything  of  military 
value.  The  British  naval  aeronautic  service,  on  the  other  hand, 
appreciated  the  futility  of  such  tremendous  and  unwieldy  construc- 
tion and,  after  a single  demonstration  of  its  uselessness,  abandoned 
it  altogether.  This  single  attempt  was  the  ill-fated  Mayfly,  which 


DIRIGIBLE  BALLOONS 


48 


was  most  appropriately  named,  since  its  performance  resolved  into 
a certainty  the  doubt  expressed  by  its  title.  In  being  taken  out 
of  its  shed,  the  framing  of  the  airship  was  damaged,  and  it  col- 
lapsed a few  minutes  later  so  that  it  never  did  fly.  One  of  the 
early  types  of  small  British  dirigibles  is  shown  in  Fig.  20. 

Attention  has  since  been  concentrated  in  most  part  on  the  con- 
struction of  aeroplanes  in  constantly  increasing  numbers,  although 
the  dirigible  has  not  been  given  up  altogether.  However,  its  restricted 
usefulness  as  well  as  the  necessary  limitations  of  its  effective  size 
has  been  recognized.  Early  in  the  war  Great  Britain  planned  the 
construction  of  fifty  small  dirigibles,  of  both  the  rigid  and  nonrigid 
types,  all  of  which  have  undoubtedly  since  been  completed.  They 
are  small  airships  designed  chiefly  for  scouting  and  short-range 
bombing  raids  over  camps  when  in  army  service  and  for  coast 
patrol  and  submarine  hunting  as  an  aid  to  the  naval  forces.  While 
no  specifications  are  available,  the  cubic  capacity  of  these  patrol 
airships  probably  does  not  exceed  50,000  to  75,000  cubic  feet,  their 
over-all  length  being  approximately  100  to  125  feet. 

Aeroplane  Features.  To  simplify  the  construction  and  at  the 
same  time  minimize  the  amount  of  head  resistance,  the  car  consists 
of  an  aeroplane  fuselage  of  the  tractor  type,  fitted  with  a compara- 
tively small  motor — under  100  horsepower — and  having  accommoda- 
tions for  a pilot  and  an  observer  in  two  cockpits,  placed  tandem. 
The  control  surfaces  are  also  similar  to  those  used  in  aeroplane 
construction.  Despite  their  low  power,  these  dirigibles  can  make 
40  miles  an  hour,  owing  to  their  greatly  reduced  head  resistance. 
Instead  of  employing  either  an  auxiliary  blowing  motor  or  a 
blower  driven  by  the  motor  itself,  the  supply  duct  to  the  air 
balloonet  is  made  rigid  and  is  sloped  forward  so  that  its  open  end 
comes  directly  in  the  slip  stream  of  the  propeller;  thus  the  latter 
serves  to  inflate  the  balloonet  as  well  as  to  drive  the  dirigible. 
The  desired  amount  of  inflation  is  controlled  by  a valve. 

Use  in  Locating  Submarines.  Many  of  these  small  scouting 
and  naval-patrol  dirigibles  have  given  a good  account  of  them- 
selves and  comparatively  few  have  met  with  accident  or  have  been 
destroyed  by  the  enemy.  On  frequent  occasions  they  have  been 
very  successful  in  locating  submarines  below  the  surface,  since  the 
body  of  the  under-water  boat  is  readily  detected  from  an  altitude 


44 


DIRIGIBLE  BALLOONS 


DIRIGIBLE  BALLOONS 


45 


of  a thousand  feet  or  more,  even 
though  submerged  to  a great 
depth  and  despite  a heavy  ripple 
on  the  surface  that  makes  the 
water  absolutely  opaque  when 
viewed  from  the  deck  of  a ship. 
Doubtless  they  will  be  employed 
to  an  increasing  extent  as  the 
hunt  for  the  submarine  becomes 
more  and  more  intensive,  though 
their  use  is  very  much  restricted 
during  the  winter  months,  owing 
to  the  frequent  and  severe  storms 
encountered. 

British  Astra=Torres.  A num- 
ber of  comparatively  small  Astra- 
Torres  dirigibles  have  also  been 
built  in  Great  Britain  for  coast 
patrol  and  anti-submarine  work. 
The.  line  drawing  at  the  left  of 
Fig.  21  illustrates  the  general 
design  and  construction  of  these 
small  airships,  while  the  various 
letters  indicate  the  different  parts 
of  the  gas  container,  air  balloon- 
ets,  suspension  and  car,  and  the 
end  view  at  the  right  of  the 
figure  rshows  the  small  amount 
of  head  resistance  offered  by  the 
suspension  of  this  type  as  com- 
pared with  that  of  the  usual  form 
of  nonrigid  dirigible.  A is  the 
balloon  itself,  or  main  gas  con- 
tainer, the  pressure  relief  valve 
for  which  is  located  at  M.  BB 
are  the  air  balloonets  connected 
with  the  blower  II  in  the  car.  In 
the  illustration  these  balloonets  are 


Fig.  21.  Side  and  End  Views  of  British  Astra-Torres  Dirigible  Used  for  Anti-Submarine  Patrol  Service 


46 


DIRIGIBLE  BALLOONS 


shown  fully  inflated  as  they  would  be  after  the  gas  bag  had  lost 
a considerable  proportion  of  its  original  contents  through  leakage 
or  expansion.  At  the  beginning  of  a flight,  when  the  gas  bag  is 
fully  inflated  with  hydrogen,  they  lie  perfectly  flat  along  the  lower 
side  of  the  envelope,  being  brought  into  service  only  as  they  are 
needed  to  keep  the  envelope  distended  to  its  full  volume. 

The  novel  method  of  suspension  to  which  this  type  of  dirigible 
owes  its  greater  speed  and  fuel  economy,  because  of  the  reduction 
of  the  head  resistance,  is  shown  by  the  numerous  supporting  ropes 
O-O-O,  which  terminate  in  a comparatively  few  cables  attached 
to  the  car.  In  the  small  British  airships  referred  to  here,  there  is 
but  one  small  car  designed  to  carry  a crew  of  two  men  and  the 
engine  is  of  comparatively  low  power,  driving  a propeller  at 
either  end  of  the  car,  but  in  the  large  French  dirigibles  of  the 
same  type,  two  large  cars  are  placed  tandem  some  distance  apart 
and  are  fitted  with  500-horsepower  motors.  The  various  parts 
indicated  by  the  letters  are:  CC  propellers,  D motor,  F space  for 
pilot  and  crew,  G fuel  and  oil  tanks,  J guide  rope,  K gas  valve, 
LL  air  valves,  NN  balloonet  cable,  P rudder,  Q stabilizer,  R R 
bracing  cables,  and  S the  car  itself. 

MILITARY  USES  OF  ZEPPELINS 

Limitations  of  Use.  Nothing  excites  the  Teutonic  imagination 
so  strongly  as  things  military  to  which  the  characteristic  German 
adjective  kolossal  can  be  enthusiastically  applied.  It  was  for  this 
reason  that,  despite  its  uniform  record  of  tragic  disaster  for  years 
before  the  war,  the  Germans  pinned  their  faith  to  the  Zeppelin  as 
a weapon  that  could  not  fail  to  strike  terror  to  the  hearts  of  the 
British  and  French  and  make  them  hasten  “to  sue  for  peace." 
However,  apart  from  its  reputed  employment  on  the  single  occa- 
sion that  the  German  grand  fleet  left  the  security  of  the  Kiel 
Canal,  it  is  not  known  to  have  been  used  in  any  purely  military 
operation.  The  aeroplane  has  been  developed  to  a point  that, 
in  spite  of  the  ability  of  the  Zeppelin  to  ascend  rapidly  when  hard 
pressed,  would  make  it  suicidal  for  one  of  the  huge  gas  bags  to 
sally  forth  in  daylight,  unless  attended  by  a large  number  of 
battle  planes  to  prevent  enemy  flying  machines  from  attacking  it. 
No  such  use  of  the  Zeppelin  has  been  recorded  thus  far.  Con- 


DIRIGIBLE  BALLOONS 


47 


sequently,  it  has  been  used  only  in  nocturnal  bomb-dropping 
expeditions,  chiefly  directed  against  London  and  only  undertaken 
when  weather  conditions  made  detection  difficult.  In  order  to 
carry  these  out,  it  has  been  necessary  to  establish  stations  in 
Belgium,  since  the  fuel  consumption  of  the  Zeppelin  is  so  great 
that,  even  with  its  tremendous  fuel  supply  of  3 to  5 tons,  a flight 
to  London  and  return  to  points  well  within  the  German  border  is 
impracticable.  The  first  raids  of  this  character  were  carried  out 
successfully,  but  subsequent  attempts  were  marked  by  the  loss 
of  one  or  two  airships  on  each  occasion,  so  that  the  practice  was 
abandoned  as  being  too  expensive  for  the  results  attained  and  aero- 
planes were  substituted. 

Number  Built.  Taking  it  for  granted  that  the  numbering  of 
the  German  airships  has  been  consecutive,  the  total  number  built 
during  the  first  three  and  one-half  years  of  the  war  by  the  Germans 
would  be  between  eighty  and  one  hundred.  All  large  German  air- 
ships have  come  to  be  commonly  termed  Zeppelins,  but  a number 
of  them  were  of  the  Schutte-Lanz  type,  almost  equally  large  and 
also  characterized  by  rigid  construction,  which,  however,  was  of 
wood  with  aluminum  fittings  instead  of  being  all  metal,  as  it  was 
found  that  the  huge  metal  frame  accumulated  a static  charge  of 
high  potential  that  was  responsible  for  igniting  the  gas  in  one  or 
two  instances. 

Weakness  of  Type.  The  L-I  ( Luftschiff , or  airship),  the  first  of 
the  German  airships  designed  for  purely  military  purposes,  was  a 
Zeppelin  525  feet  long  by  50  feet  in  diameter,  of  777,000  cubic 
feet  capacity,  and  22  tons  displacement.  Its  three  sets  of  motors 
developed  500  horsepower  and  it  had  a speed  of  52  miles  per 
hour.  It  wTas  launched  at  Friedrichshafen  in  1912,  and  after  a 
number  of  successful  cross-country  trips,  it  was  tried  in  connec- 
tion with  naval  maneuvers  off  Heligoland.  Before  the  trial  had 
proceeded  very  far,  a sudden  squall  broke  the  backbone  of  the 
huge  gas  bag  and  hurled  it  into  the  sea,  drowning  fifteen  out  of 
the  crew  of  twenty-two.  It  is  a striking  commentary  on  the 
frailness  of  these  aerial  monsters  that  every  one  of  the  big  airships 
built  up  to  that  time  had  met  disaster  in  an  equally  sudden 
manner  but  from  a totally  different  cause  in  each  instance.  The 
L-II  was  slightly  shorter  but  had  5 feet  longer  beam  and  dis- 


48 


DIRIGIBLE  BALLOONS 


placed  27  tons.  She  was  designed  particularly  for  naval  use,  had 
four  sets  of  motors  developing  900  horsepower,  and  was  fitted  with 
a navigating  bridge  like  that  of  a ship.  It  was  confidently  thought 
that  all  possible  shortcomings  had  been  remedied  and  success 
finally  achieved  in  the  L-II,  but  before  there  was  any  opportunity 
to  demonstrate  its  efficiency,  the  airship  exploded  in  mid-air,  killing 
its  entire  crew. 

Effectiveness  Grossly  Overrated.  Despite  this  unbroken  chain 
of  disasters,  the  German  official  press  bureau  spread  broadcast 
the  prowess  of  the  Zeppelin,  its  magnificent  ability,  and  its  remark- 
able achievements  as  an  engine  of  war — in  theory,  since  this  was  a 
year  or  two  prior  to  the  outbreak  of  hostilities.  Had  it  not  been 
for  the  forced  descent  of  the  Zeppelin  IV  at  Luneville,  where  it 
was  taken  possession  of  by  the  French,  these  tales  might  have 
been  accepted  at  their  face  value.  But  the  log  of  the  commander 
of  this  airship  showed  that  its  maximum  speed  was  but  45  miles 
per  hour,  the  load  10,560  pounds,  and  the  ascensional  effort  45,100 
pounds.  The  fuel  consumption  averaged  297  pounds  per  hour 
while  the  fuel  capacity  was  only  sufficient  for  a flight  of  seven 
hours.  During  its  flight,  it  had  reached  an  altitude  of  only  6,250 
feet,  to  accomplish  which  over  3 tons  of  ballast  had  to  be  dropped. 
It  was  also  shown  that  the  critical  flying  height  of  these  huge  air- 
ships is  between  3,500  and  4,000  feet,  Zeppelin  himself  declaring 
that  his  machines  were  useless  above  5,000  feet.  This  probably 
accounts  for  the  fact  that  the  early  raids  on  English  towns  were 
carried  out  at  a height  but  slightly  in  excess  of  2,000  feet.  Later 
types,  however,  are  said  to  have  reached  high  altitudes. 

Shortly  before  the  outbreak  of  the  war  the  L-5  was  completed. 
This  had  a capacity  of  about  1,000,000  cubic  feet,  motors  aggre- 
gating 1,000  horsepower  or  over,  and  a reputed  speed  .of  65  miles 
per  hour.  Just  what  was  the  fate  of  this  particular  ship  did  not 
become  known,  since  information  of  a military  character  has  not 
been  permitted  to  leak  out  of  Germany  from  that  time  on.  But 
capture  or  destruction  has  accounted  for  many  of  the  intermediate 
numbers  of  the  series;  big  German  airships  have  been  brought 
down  in  England,  in  the  North  Sea,  in  France,  and  at  Saloniki, 
their  loss  culminating  in  the  disaster  to  four  out  of  the  fleet  of  fix  e 
that  attempted  a raid  over  London  but  were  caught  by  adverse 


DIRIGIBLE  BALLOONS 


49 


Fig.  22.  Zeppelin  L-49  Brought  Down  Intact  by  a French  Airman,  Resting  on  Hillside  near  Bourbon-Les-Baines 
Copyright  by  Underwood  and  Underwood,  New  York 


50 


DIRIGIBLE  BALLOONS 


winds  which  exhausted  their  fuel  supply  so  that  they  were  blown 
out  of  control,  toward  the  south  of  France.  French  anti-aircraft 
batteries  or  aeroplanes  accounted  for  three  of  these,  while  the 
fourth,  the  L-49,  was  captured  intact. 

L=49.  An  essential  part  of  the  equipment  of  every  form  of 
German  military  apparatus  is  a means  of  destroying  it  in  case  of 
capture.  In  the  case  of  the  big  airships,  the  officers  are  provided 
with  revolvers  loaded  with  incendiary  bullets,  which  are  fired  into 


Fig.  23.  Nose  of  Giant  L-49  and  Group  of  Sightseers 
Copyright  by  Underwood  and  Underwood , New  York 


the  gas  bag,  so  that  until  the  L-49  was  forced  to  descend  in  the 
south  of  France  by  the  activities  of  a battle  plane,  plus  a lack  of 
fuel,  no  airship  of  a recent  type  had  ever  been  captured  intact. 
In  this  case,  the  commander  fired  his  pistol  at  the  balloon  but 
missed  and  was  prevented  from  firing  again  by  a French  peasant 
who  “covered”  him  with  a shotgun.  The  wireless  operator  suc- 
ceeded in  using  a sledge  hammer  on  some  of  the  apparatus  of  the 
very  completely  equipped  wireless  cabin  before  he  was  captured 


DIRIGIBLE  BALLOONS 


51 


but  did  not  do  sufficient  damage  to  prevent  reassembly  of  the 
parts  with  little  trouble.  With  the.  exception  of  the  earlier  type 
of  Zeppelin  that  was  forced  to  descend  at  Luneville  prior  to  the 
war,  the  L-49  was  the  first  that  was  ever  known  to  have  landed 
undamaged  in  hostile  territory,  as  practically  all  the  others  were 
destroyed  in  the  air,  most  of  them  having  been  wrecked  either  by 
aeroplane  or  anti-aircraft  fire.  Fig.  22  shows  the  L-49  as  it  rested 
on  a hillside  at  Bourbon-les-Baines,  France,  and  Fig.  23  shows  a 
close  view  of  the  nose  of  the  monster. 

Standardized  Parts.  Comparing  the  L-49  with  many  of  its 
predecessors  led  to  the  conclusion  that  it  was  one  of  the  latest 
types,  but  an  inspection  of  its  construction  revealed  the  use  of 
many  parts  produced  in  quantities  from  standard  patterns  as  well 
as  a lack  of  the  finish  that  has  always  characterized  airship  con- 
struction. Appearance  and  comfort  had  both  been  sacrificed  with 
a view  to  saving  the  last  ounce  of  superfluous  weight  in  order  to 
carry  more  fuel  and  ammunition.  Evidently  the  production  of 
these  large  airships  has  been  reduced  to  a manufacturing  basis  and 
they  are  constructed  in  series  in  much  the  same  manner  as  motor 
cars,  though  on  a reduced  scale. 

General  Design.  In  its  general  construction  the  L-49  was 
along  the  same  lines  that  have  characterized  the  Zeppelin  since  its 
inception,  the  outer  envelope  being  stretched  over  a rigid  frame  of 
aluminum  girders,  inclosing  a large  number  of  independent  balloons 
inflated  with  the  usual  hydrogen  gas,  no  trace  being  discovered  of 
the  non-inflammable  gas,  the  discovery  of  which  had  been  hailed 
by  the  German  press.  The  commander’s  cabin  was  suspended 
well  forward  with  the  wireless  room  directly  behind  it,  while  a 
V-shaped  gangway,  recessed  in  the  envelope  proper  so  as  to  present 
no  additional  head  resistance,  ran  back  from  the  latter  the  whole 
length  of  the  ship.  This  and  the  gun  platform  on  top,  mounting 
two  machine  guns  and  reached  by  a ladder  suspended  in  a well 
amidships,  have  been  familiar  features  of  all  the  recent  Zeppelins. 
The  main  envelope  contained  nineteen  independent  gas  bags,  each  of 
which  was  made  integral  with  an  air  balloonet  to  take  care  of  the 
expansion  and  contraction  of  the  hydrogen  with  varying  altitudes 
and  temperatures.  Distributed  along  the  lower  part  of  the  frame 
inside  the  envelope  were  a series  of  50-gallon  water-ballast  tanks. 


52 


DIRIGIBLE  BALLOONS 


Power  Plant.  No  less  than  nine  large  motors  were  employed 
to  drive  the  huge  gas  bag,  the  maximum  horsepower  probably 
aggregating  1,600  to  2,000.  The  motors  were  distributed  in  five 
different  locations,  the  largest  being  suspended  just  abaft  the 
wireless  room.  The  remainder  were  placed  in  self-contained  units 
in  the  form  of  gondolas  suspended  from  the  sides  of  the  frame,  as 
shown  in  Fig.  24,  the  outline  being  that  of  a blunt-nosed  fish. 
Each  of  these  gondolas  carried  two  motors  placed  side  by  side 
and  coupled  up  so  that  either  one  or  both  could  be  employed  to 
drive  the  single  propeller.  For  cruising  speeds  one  motor  in  each 
gondola  supplied  sufficient  power  or  in  some  gondolas  both  motors 
could  remain  idle.  No  accommodation  was  provided  for  attendants 
in  the  gondolas,  any  of  which  could  easily  be  reached  by  light 
ladders  from  the  inclosed  gangway. 

To  insure  greater  safety,  the  fuel  supply  was  divided  among 
sixteen  tanks,  all  of  which  were  interconnected  with  each  other 
and  the  engines  so  that  gasoline  from  any  tank  or  tanks  could  be 
diverted  to  any  particular  engine.  The  supply  of  lubricating  oil 
for  each  engine  was  carried  in  a tank  in  the  gondola  itself. 

Control.  Vertical  and  horizontal  stabilizing  surfaces  of  conven- 
tional form  were  built  on  the  sharply  tapering  rear  end  of  the 
frame,  the  elevator  and  rudder  being  similar  to  those  used  in 
aeroplane  construction,  except  that  the  rudder  was  in  two  sections, 
the  larger  of  which  was  placed  on  top  of  the  envelope.  The  con- 
trol of  these  surfaces,  the  operation  of  all  the  engines,  the  control 
of  the  water  ballast,  the  air  supply  to  the  balloonets,  and  the  fuel 
supply  to  the  motors  were  all  concentrated  at  a panel  board  in  the 
commander’s  cabin,  the  forward  end  of  which  bore  a close  resem- 
blance to  the  bridge  of  a man-of-war.  By  means  of  thirty-eight 
push  buttons,  half  red  and  half  white,  air  could  be  released  from 
or  pumped  into  the  balloonets,  while  in  a similar  manner  the 
contents  of  any  one  of  the  water-ballast  tanks  could  be  emptied. 
Elaborate  controls  were  provided  for  the  power  plant,  it  being 
possible  to  vary  the  speed  or  stop  any  one  or  more  of  the  motors 
from  the  bridge.  The  rudder  and  elevators  were  operated  by 
means  of  small  hand  wheels,  similar  to  a marine  steering  wheel. 
One  of  the  most  prominent  features  of  the  operating  cabin  was  a 
huge  chart  frame,  capable  of  carrying  a large  scale  map  covering  a 


DIRIGIBLE  BALLOONS 


53 


considerable  area,  as  well  as  an  ample  supply  of  maps.  Few 
instruments  were  found  in  the  captured  ship  and  it  is  thought 


Fig.  24.  One  of  Six  Gondolas,  or  Power  Units  of  the  Zeppelin  L-49 
Copyright  by  Underwood  and  Underwood , New  York 

highly  probable  that  everything  not  fastened  in  place  had  been 
dumped  overboard  at  the  last  to  increase  its  lifting  power. 


54 


DIRIGIBLE  BALLOONS 


Apart  from  the  use  of  standardized  fittings  and  parts  and  the 
employment  of  a great  deal  more  power  in  a slightly  different 
manner  than  had  characterized  the  earlier  types  of  Zeppelins,  the 
L-49  revealed  nothing  of  unusual  importance  in  airship  design  and 
certainly  none  of  the  world-beating  features  that  German  propa- 
ganda had  been  heralding  for  some  time  previous. 

Destruction  of  Zeppelins.  Mention  has  already  been  made  of 
the  fact  that  practically  the  only  use  made  by  Germany  of  her 
huge  airships  has  been  the  bombardment  of  open  cities,  and  that 
always  at  night.  From  the  first  of  September,  1914,  up  to  the 
end  of  1917,  between  thirty  and  forty  had  met  disaster,  but  only 
two  were  captured  intact.  The  first  of  these  was  discovered  by  a 
Russian  cavalry  patrol  while  at  anchor  and  its  crew  of  thirty  men 
were  made  prisoners.  This  was  at  an  early  period  in  the  war, 
while  the  second  one  to  be  captured  was  the  L-49,  already  referred 
to,  which  formed  one  of  a squadron  of  five  evidently  sent  out  on 
a bombing  expedition  against  London.  Owing  to  adverse  winds, 
they  never  reached  their  destination  and  four  of  them  were  known 
to  have  been  put  out  of  action,  all  except  the  L-49  being  destroyed 
in  the  air.  Not  a few  of  these  big  airships  have  fallen  victims  to 
their  own  weakness  and  succumbed  to  the  elements,  in  one  instance 
a high  wind  tearing  the  airship  loose  from  its  moorings  while  the 
crew  was  not  aboard.  This  was  at  Kiel,  and  after  traveling  a 
number  of  miles  unguided,  the  big  bag  fell  into  the  North  Sea. 
In  quite  a number  of  other  cases  head  winds  have  prevented  the 
return  of  the  raiders  to  their  base  and  they  have  either  been 
destroyed  by  their  crews  or  wrecked  at  sea  in  attempting  to  return. 
In  still  other  instances  the  unwieldy  monsters  have  been  wrecked 
by  high  winds  when  attempting  to  land,  as  was  so  frequently  the 
case  prior  to  the  war. 

Aeroplane  and  Anti- Aircraft  Fire  Effective.  Before  the  war 
broke  out  the  ability  of  either  the  aeroplane  or  the  anti-aircraft 
gun  to  overcome  the  Zeppelin  was  purely  theoretical,  but  actual 
experience  has  demonstrated  that  much  of  the  theory  was  well 
founded.  x\t  least  three  Zeppelins  have  been  destroyed  by  British 
aviators  in  mid-air,  all  or  most  of  the  crews  being  killed,  while 
probably  an  equal  number  have  been  accounted  for  by  French 
aviators  in  open  battle.  The  war  had  not  been  under  way  a 


DIRIGIBLE  BALLOONS 


55 


month  before  French  anti-aircraft  gunners  showed  their  skill  by 
bringing  down-a  “Zep,”  while  only  a week  later  a Russian  battery 
accomplished  the  same  feat,  in  this  instance  killing  the  entire  crew. 
In  1916,  British  and  French  gunners  succeeded  in  either  “winging” 
or  setting  on  fire  three  or  four,  while  two  dropped  into  the  North 
Sea  and  one  was  blown  up  by  its  crew,  having  run  out  of  fuel 
while  raiding  Scotch  towns. 

Bombing  Raids  against  Zeppelin  Sheds.  Not  the  least  of  the 
disadvantages  from  which  such  huge  and  unwieldy  craft  suffer  is 
the  fact  that  the  correspondingly  large  structures  required  to 
house  them  make  exceedingly  easy  marks  for  the  raiding  aviator. 
Bombing,  however,  is  such  an  uncertain  art  that  even  such  large 
buildings  as  these  cannot  be  struck  from  any  altitude  with  a fair 
degree  of  accuracy.  Consequently,  in  the  number  of  raids  that 
have  been  carried  out  against  Zeppelin  sheds,  success  has  been  due 
very  largely  to  the  temerity  of  the  aviators,  who  have  descended 
within  a few  hundred  feet  of  their  mark  despite  the  fire  directed 
at  them  from  all  quarters.  At  least  three  and  probably  more  of 
the  big  airships  have  been  destroyed  in  this  manner  by  British 
aviators,  who  have  made  flights  of  several  hundred  miles  to  reach 
their  destination,  while  the  destruction  of  as  many  more  has  been 
ascribed  by  the  Germans  to  the  “accidental”  explosion  of  a bomb 
in  the  shed.  In  view  of  the  great  precautions  taken  against 
accident  from  the  explosion  of  the  bombs  carried  by  the  airship 
itself,  it  is  not  considered  at  all  likely  that  there  was  anything 
accidental  about  the  wrecking  of  these  craft. 

One  of  the  earliest  attempts  against  Zeppelin  headquarters  at 
Friedrichshafen  on  Lake  Constance,  which  resulted  in  the  destruc- 
tion of  the  L-31,  is  typical  of  the  plan  followed  in  attacks  of 
this  kind.  Two  British  aviators  flew  from  their  base  in  France, 
about  250  miles  distant,  at  a high  altitude.  They  became  sepa- 
rated before  reaching  their  destination  owing  to  a mist.  This, 
however,  prevented  their  discovery  until  they  had  dropped  within 
a few  hundred  feet  of  the  surface  of  the  lake,  which  it  was  neces- 
sary to  do  to  obtain  a view  of  the  airship  sheds.  The  first  pilot 
dropped  his  cargo  of  bombs  from  a height  of  only  100  feet  or  so 
over  the  shed  and  was  rewarded  by  seeing  it  catch  fire.  He  had 
hardly  straightened  out  on  his  return  course  before  he  heard  the 


56 


DIRIGIBLE  BALLOONS 


attack  of  his  companion.  The  latter  was  not  so  fortunate  in 
escaping  unscathed,  as  a bullet  pierced  his  fuel  tank  and  compelled 
him  to  descend.  In  the  majority  of  instances,  however,  the  raiders 
have  succeeded  not  only  in  carrying  out  their  task  but  in  escaping 
undamaged  as  well. 


CAPTIVE  BALLOONS 

Military  Value.  As  an  aid  to  military  operations,  the  use  of 
the  captive  balloon  dates  back  many  years.  It  was  extensively 
employed  in  the  Civil  war  and  more  recently  in  the  Boer  war, 
but  with  the  advent  of  both  the  dirigible  and  the  aeroplane,  it 
was  generally  considered  outside  of  Germany  that  its  reason  for 
existence  had  passed  away.  The  German  military  plans  included 
a large  number  of  balloons  for  artillery  observation  purposes  and 
they  were  used  right  from  the  start.  It  was  only  when  the  fight- 
ing settled  down  to  trench  warfare,  however,  that  they  came  into 
prominence  and  the  aid  that  they  rendered  the  German  batteries 
put  their  opponents  at  a serious  disadvantage.  Like  the  bayonet, 
which  was  also  generally  considered  to  have  been  relegated  to 
military  operations  of  the  past,  the  captive  balloon  is  now  playing 
a very  important  role,  particularly  on  the  western  front.  In  favor- 
able weather,  anywhere  from  ten  to  forty  of  these  aerial  observation 
posts  will  be  visible  from  a single  point  on  the  line. 

Spherical  Type  Defective.  The  captive  balloon  of  the  present 
day,  however,  bears  no  resemblance  to  its  predecessors.  From  a 
sphere,  it  has  been  developed  into  a form  that  more  nearly  resembles 
the  dirigible  and  at  the  same  time,  it  embodies  some  of  the  features 
of  the  aeroplane.  The  old  spherical  balloon  was  always  at  the  mercy 
of  the  wind,  which  not  only  governed  the  altitude  to  which  the  balloon 
would  rise  but  also  made  things  extremely  uncomfortable  as  well  as 
dangerous  for  the  observers.  With  1,000  feet  of  cable  out,  such  a 
balloon  rises  to  an  equivalent  height  on  a perfectly,  calm  day.  But 
even  a light  wind  cuts  this  height  down  by  100  or  200  feet,  while 
if  a strong  wind  is  blowing,  the  balloon  is  held  down  to  within  a 
few  hundred  feet  of  the  ground  regardless  of  the  length  of  cable 
paid  out.  Every  strong  gust  beats  it  over  at  a perilous  angle  and 
the  resulting  shocks  to  the  basket  are  so  severe  that  its  occupants 
can  have  little  thought  for  anything  but  their  own  safety.  Strong 


DIRIGIBLE  BALLOONS 


57 


cross  gusts  set  both  the  bag  and  basket  to  spinning  and  jumping  in 
a manner  that  would  make  the  results  of  the  severest  storm  at  sea 
seem  mild  by  comparison,  since  the  movements  of  the  basket  are 
executed  with  such  rapidity  that  they  seem  to  be  in  almost  every 
plane  simultaneously.  As  a result,  the  old  type  of  captive  balloon 
was  available  for  service  only  in  the  calmest  weather. 

Modern  Kite  Balloon.  It  should  not  be  supposed  that  the 
improved  type  of  observation  balloon  now  in  use  in  such  large 
numbers  provides  any  unusual  amount  of  ease  or  comfort,  since 
it  is  also  prey  to  the  wind  and  does  a great  deal  of  swinging  about 
as  well  as  jerking  when  the  wind  is  more  than  15  or  20  miles  an 
hour.  But  it  has  been  improved  to  a point  where  the  wind  not 
only  serves  to  elevate,  instead  of  depressing  it,  but  also  to  steady 
it.  The  new  type.  Fig.  25,  is  technically  known  as  a kite  balloon, 
because,  in  addition  to  the  appendages  attached  to  the  bag  itself  for 
steadying  purposes,  it  is  equipped  with  a tail  to  assist  in  keeping 
it  heading  into  the  wind.  This  consists  of  a number  of  bucket- 
shaped pieces  of  heavy  canvas  attached  to  the  tail  cable  by 
bridles  so  as  to  catch  the  wind  and  hold  it,  thus  placing  a heavy 
strain  on  the  cable  and  preventing  the  balloon  from  swinging 
violently.  As  is  the  case  with  practically  everything  used  at  the 
front,  the  technical  name  of  the  new  type  of  balloon  is  prominent 
by  its  absence.  It  is  a Drache  (kite)  to  the  Germans  and  a “blimp” 
to  Tommy  Atkins.  Both  its  shape  and  attitude  when  aloft  bear  a 
close  resemblance  to  a huge  sausage,  so  that  the  term  “sausage”  is 
used  by  all  the  belligerents  in  common  to  a large  extent.  A side 
view  of  an  American  type  is  shown  in  Fig.  26. 

It  will  be  noted  from  Figs.  25  and  26  that  the  suspension  of 
the  basket  and  the  appendages  attached  to  the  balloon  at  the  rear 
hold  it  in  a position  which  is  roughly  the  equivalent  on  a large  scale 
of  the  curve  of  an  aeroplane  wing.  It  has  both  camber  and  an  angle 
of  incidence,  so  that  the  wind  serves  to  elevate  it  instead  of  beat- 
ing it  down.  This  lifting  effect  is  further  increased  by  tubes  of 
large  diameter,  open  at  the  forward  end  only  and  curving  around 
the  end  of  the  gas  bag  at  the  rear.  (It  is  also  equipped  with  an 
air  balloonet,  the  same  as  a dirigible.)  The  wind  enters  the  lower 
end  of  this  tubular  member,  which  is  in  a line  with  the  longitu- 
dinal axis  of  the  balloon,  but  it  must  pass  around  the  curve  at 


Fig.  25.  Head-On  View  of  Modern  Kite  Balloon, 
Showing  Details  of  Tail  Buckets 
Copyright  by  Central  News  Service , New  York  City 


DIRIGIBLE  BALLOONS 


59 


the  end  of  the  gas  bag  before  it  can  fully  inflate  it,  so  that  it 
performs  the  double  function  of  increasing  the  lift  and  steadying 


Fig.  26.  American  Kite  Balloon  of  Latest  Type  Ascending 
Copyright  by  Committee  on  Public  Information , Washington,  D C. 


the  balloon,  though  the  latter  is  its  chief  purpose.  The  basket  is 
suspended  quite  a distance  below  the  gas  bag  and  has  accommoda- 


60 


DIRIGIBLE  BALLOONS 


tion  for  two  observers.  Like  scores  of  other  inventions  that  the 
Germans  were  the  first  to  utilize  on  a large  scale  in  the  present  war, 
the  kite  balloon  was  not  a German  creation  but  was  originally 
developed  in  France. 

Methods  of  Inflation.  The  average  capacity  of  the  kite 
balloons  used  for  observation  purposes  is  28,000  cubic  feet.  They 
are  inflated  with  hydrogen  either  from  a portable  generating  plant 
forming  part  of  the  equipment  of  the  balloon  company  or  from  a 
supply  carried  under  high  pressure  in  heavy  steel  “bottles”  similar 
to  those  used  for  transporting  oxygen  or  carbonic  acid  gas  intended 
for  industrial  use.  Since  the  balloon  companies  are  stationed  about 
4 miles  back  of  the  firing  line,  the  use  of  the  portable  plant  is 
practical,  but  it  has  been  found  more  economical  and  more  con- 
venient to  generate  the  gas  on  a large  scale  at  special  establish- 
ments in  France  and  England  and  send  it  to  the  front  in  containers. 
With  a portable  plant,  several  hours  are  necessary  to  inflate  the 
gas  bag,  whereas  with  a large  supply  of  the  gas  at  hand  under 
high  pressure,  the  operation  may  be  carried  out  in  less  than  an  hour. 

The  balloon  naturally  works  under  the  same  difficulties  as 
all  lighter-than-air  craft,  that  is,  there  is  a constant  leakage  of 
the  hydrogen  through  the  fabric  in  addition  to  that  lost  by  the 
expansion  of  the  gas  on  warm  days  when  the  summer  sun  beats 
down  directly  on  the  gas  bag.  Where  a field  generating  plant  is 
employed,  quick  inflation  of  a new  balloon  or  replacement  of  loss 
is  accomplished  by  the  used  of  several  “nurses”,  Fig.  27.  These  are 
simply  large  gas  bags  which  are  kept  replenished  by  the  gas  plant 
working  constantly,  in  other  words,  they  are  storage  tanks,  and 
when  it  is  necessary  to  inflate  the  balloon  quickly,  their  contents 
are  simply  transferred  to  it. 

Balloon  Company.  Though  aeronautical  in  character,  the  kite 
balloon  service  is  actually  a branch  of  the  artillery,  to  which  it  is 
directly  attached.  A balloon  company  accordingly  consists  of 
twelve  to  twenty  artillery  officers  of  varying  ranks  and  about  120 
to  130  men.  Of  the  officers,  six  to  eight  are  artillery  lieutenants  or 
captains  and  go  aloft  as  observers,  this  number  being  necessary 
because  the  strain  of  watching  constantly  is  very  great  and  the 
observers  must  be  relieved  at  frequent  intervals,  the  balloon  other- 
wise being  kept  up  continuously,  both  day  and  night.  There  are 


DIRIGIBLE  BALLOONS  61 


Fig.  27.  Landing  Big  Kite  Balloon  at  Training  Station  “Somewhere  in  England.”  "Nurse”  in  Background 
Copyright  by  Underwood  and  Underwood,  New  York 


62 


DIRIGIBLE  BALLOONS 


also  a number  of  sergeants,  each  of  whom  is  in  charge  of  a differ- 
ent branch  of  the  work,  such  as  the  inflation,  transport,  telephone 
service,  and  winding  machine.  No  less  than  fifteen  3-ton  to  5-ton 
motor  trucks  are  necessary  for  each  balloon  company  besides  two 
or  more  motorcycle  messengers,  the  care  of  the  machines  usually 
being  entrusted  to  the  corporals  of  the  company.  The  remainder 
of  the  company  are  practically  laborers,  whose  chief  duties  are  to 
attach  the  ballast  bags  to  the  ropes  when  it  is  intended  to  hold 
the  balloon  on  the  ground  for  any  length  of  time  and  to  utilize 
their  own  weight  for  the  same  purpose  when  the  balloon  is  about 
to  go  aloft  or  is  only  on  the  ground  temporarily.  In  addition, 
every  company  has  its  surgeon  and  assistants,  quartermaster,  cooks, 
company  clerk!  and  other  attaches  necessary  to  complete  its  organ- 
ization, since  a balloon  company  serves  as  an  independent  unit. 

Equipment.  The  paraphernalia  required  is  quite  as  elaborate 
as  that  necessary  to  keep  several  aeroplanes  aloft,  though  naturally 
of  a different  nature.  It  must  all  be  readily  portable,  for  a balloon 
company  has  to  change  camp  more  or  less  frequently,  or  as  often 
as  the  enemy  artillery  happens  to  discover  its  range.  To  secure 
mobility  is  the  purpose  of  the  great  number  of  motor  trucks 
employed.  One  of  these  is  equipped  with  a hoisting  winch  and  a 
large  drum  capable  of  holding  3,000  or  4,000  feet  of  about  f-inch 
steel  cable.  The  winch  is  driven  by  the  same  engine  that  propels 
the  truck,  and  in  case  of  emergency  the  engine  may  be  applied  to 
the  two  purposes  alternately  within  a short  space  of  time.  For 
instance,  in  case  of  attack  either  by  shrapnel  from  an  enemy 
battery  or  by  a hostile  aviator,  it  may  be  used  to  quickly  haul  in 
or  let  out  cable  to  change  the  altitude  of  the  balloon,  or  it  may  be 
employed  to  drive  the  truck  to  another  and  more  favorable  loca- 
tion with  the  balloon  in  tow. 

Another  truck  houses  a complete  telephone  exhange,  since  the 
observers  in  the  balloon  may  wish  to  communicate  with  any  one 
of  a number  of  batteries  which  they  are  serving.  Telephone 
communication  is  established  by  means  of  an  insulated  wire  which 
forms  the  core  of  the  cable,  while  the  steel  cable  itself  acts  as  the 
return  wire  to  complete  the  circuit.  In  some  cases,  a separate 
copper  cable  is  employed,  using  the  steel  cable  as  the  return  half 
of  the  circuit.  In  addition  there  is  a truck  for  transporting  the 


DIRIGIBLE  BALLOONS 


63 


balloons,  for  the  company  must  always  have  duplicate  equipment 
at  hand  in  case  of  the  destruction  of  the  balloon  it  is  using  or,  as 
more  frequently  happens,  damage  of  a nature  that  requires  hours  or 
days  to  repair.  In  addition  to  the  balloon  itself,  there  are  covers 
and  the  ground  cloth,  as  in  inflating  a balloon  no  part  of  its  fabric 
must  be  allowed  to  touch  the  ground  because  of  the  danger  of  stones 
or  sticks  tearing  rents  in  it.  The  balloon  proper  and  its  immediate 
accessories  utilize  at  least  one  and  sometimes  two  motor  trucks. 

To  hold  the  balloon  on  the  ground  when  out  of  service,  there 
are  eighty  sacks  of  sand  weighing  25  pounds  each,  or  an  aggregate 
of  1 ton  of  ballast,  in  addition  to  which  there  are  necessary  a 
large  number  of  steel  screw  stakes,  spare  ropes  and  parts,  ladders 
and  the  like,  besides  the  basket  and  its  equipment.  The  stakes 
are  employed  to  hold  the  balloon  down  in  a heavy  wind  by  “peg- 
ging” it  in  the  same  manner  as  a tent.  Three  or  four  trucks  are 
required  to  carry  the  large  supply  of  hydrogen  necessary,  which 
entails  the  transportation  of  130  to  150  containers.  Each  container 
holds  several  thousand  cubic  feet  of  gas  under  high  pressure,  which 
is  released  through  a reducing  valve.  Some  of  the  other  transpor- 
tation units  required  are  the  “cook  wagon,”  quartermaster’s  stores 
truck,  truck  for  carrying  tents,  blankets,  and  other  impediments  for 
the  men,  and  the  “doctor’s  wagon”  (ambulance). 

Advantages  of  Kite  Balloon.  It  became  a necessity  to  resur- 
rect the  captive  balloon  and  bring  it  up  to  date,  not  simply 
because  the  Germans  were  employing  it  in  numbers,  but  because 
experience  demonstrated  that  it  possessed  numerous  advantages 
over  the  aeroplane  for  artillery  observation.  The  observer  in  an 
aeroplane  is  carried  back  and  forth  over  and  around  the  location 
he  wishes  to  watch,  at  high  speed  and  at  a constantly  varying 
altitude.  He  must  communicate  by  means  of  either  signals  or 
wireless,  and  it  is  not  always  possible  for  him  in  either  case  to 
know  whether  his  signals  have  been  received  and  understood, 
since  it  is  possible  to  transmit  messages  by  wireless  from  an 
aeroplane  but  a very  difficult  matter  to  receive.  The  observers  in 
a kite  balloon,  on  the  other  hand,  have  the  advantage  of  being 
able  to  scrutinize  a certain  sector  constantly  with  the  aid  of  pow- 
erful glasses.  With  a few  weeks  of  experience  in  observing  a given 
terrain  they  become  so  familiar  with  it  that  any  changes  or  the 


64 


DIRIGIBLE  BALLOONS 


movements  of  troops  or  supplies  are  quickly  distinguished.  The 
greatest  advantage,  however,  is  that  the  information  thus  acquired 
may  be  instantly  transmitted  not  merely  to'  one  but  to  any  one 
or  all  of  a group  of  batteries  extending  over  a mile  or  two  of 
front  in  either  direction,  the  balloons  being  stationed  4 to  6 
miles  apart.  The  observers  are  fitted  with  portable  head  sets  so 
that  they  speak  directly  into  their  telephones  without  the  neces- 
sity of  removing  the  glasses  from  their  eyes,  which  enables 
them  to  watch  the  fall  of  the  shells  and  tell  the  battery  attend- 
ant in  the  dugout  alongside  the  gun  whether  a shell  fell  “short”, 
“over,”  “left,”  or  “right,”  and  the  amount  of  correction  needed 
before  the  smoke  from  the  explosion  has  cleared  away.  With 
the  aid  of  close  corrections  of  this  nature  the  battery  com- 
mander is  in  a position  to  get  the  range  exactly  without  the 
great  expenditure  of  ammunition  that  firing  entirely  by  map  or 
with  the  assistance  of  aeroplane  observers  entails.  Instances  are 
recorded  in  which  a 9.5-inch  shell  has  been  landed  right  in  a 
concrete  “pill-box”  not  over  15  feet  square  from  a distance  of 
3 miles  after  six  trial  shots  had  been  fired  to  obtain  the  range. 
Such  a shot  is  reported  back  to  the  battery  by  the  balloon 
observer  as  a “direct  hit,”  and  it  is  only  necessary  to  fire  the  gun 
at  the  same  range  and  direction  to  score  as  often  as  necessary. 

Duties  of  Balloon  Crew.  Each  kite  balloon  carries  aloft  two 
observers,  Fig.  28,  both  of  whom  can  concentrate  their  entire  atten- 
tion on  the  work  of  “spotting,”  since  they  have  nothing  to  do  with 
the  control  of  the  balloon  itself,  except  to  give  orders.  Their  chief 
duties  consist  of  “counter-battery”  observation,  that  is,  spotting 
the  location  of  enemy  batteries,  and  being  constantly  alert  to 
detect  any  suspicious  movements  back  of  the  enemy’s  lines,  such 
as  movements  of  troops,  ammunition,  or  supplies.  The  batteries 
controlled  from  observation  balloons  are  the  “heavies,”  which  are 
located  1 mile  or  more  back  of  the  front  line  trenches  and  to  the 
gunners  of  which  the  objects  they  are  firing  at  are  never  visible. 
Some  of  the  heaviest  guns  mounted  on  specially  constructed  rail- 
way trucks  are  often  fired  from  points  5 miles  or  more  back  of 
the  lines.  In  fact,  when  balked  in  their  attempt  to  take  Calais,  the 
Germans  bombarded  the  town  with  the  aid  of  long-range  naval 
guns  from  a distance  of  over  15  miles  and  every  shot  dropped 


DIRIGIBLE  BALLOONS 


G5 


into  either  some  part  of  the  city  or  its  outskirts.  Buildings,  hills, 
or  specially  constructed  and  concealed  observation  towers  are 
frequently  utilized  in  conjunction  with  captive  balloons  to  serve 
as  auxiliary  observation  posts,  so  that  the  base  line  connecting  the 
two  may  be  used  to  triangulate  distances  and  thus  calculate  them 
more  accurately  than  is  possible  by  direct  observation  from  a 
single  point. 

Risks  Incurred.  Enemy  Fire.  While  the  observers  in  a kite 
balloon  are  not  subjected  to  all  the  risks  that  the  aviator  must 


Fig.  28.  French  Kite  Balloon  Observers  about  to  Ascend 
Copyright  by  Committee  on  Public  Information,  Washington,  D.C. 


encounter  when  he  goes  aloft  or,  at  least,  not  to  the  same  extent, 
their  lot  is  far  from  being  free  from  danger.  One  of  the  duties 
of  the  reconnoitering  aviator  is  to  destroy  observation  balloons  by 
means  of  incendiary  bombs  equipped  with  fishhooks  which  catch 
in  the  fabric  or  by  the  use  of  his  machine  gun.  Enemy  batteries 
may  also  succeed  in  getting  the  range  of  the  balloon  and  fire  at  it 
with  large  caliber  shrapnel,  which  spreads  its  fragments  over  an 
area  100  yards  or  more  in  diameter  when  it  bursts.  So  many  of 
the  German  balloons  were  downed  by  French  and  British  aviators 


GG 


DIRIGIBLE  BALLOONS 


in  the  early  part  of  the  war — and  the  Germans  retaliated  in  kind — 
that  a battle  plane  is  now  always  detailed  to  keep  watch  above  the 
balloon  to  ward  off  attacks  by  aeroplanes. 

Escape  of  Balloon.  In  addition  to  the  risk  of  being  shot  down, 
there  is  the  ever-present  danger  of  the  balloon  being  wrecked  by  a 
sudden  squall  or  of  its  breaking  away  from  its  windlass  through  the 
parting  of  the  cable  and  floating  over  the  enemy  lines.  Balloons 
have  been  lost  through  both  causes  in  a number  of  instances.  Each 
of  the  two  observers  wears  a heavy  harness  to  which  is  attached  a 
parachute  suspended  by  a light  cord  from  the  rigging  of  the  balloon, 
so  that  in  case  of  emergency  they  may  save  themselves  by  jumping 
without  having  to  make  any  preparations  for  their  sudden  drop. 

In  case  of  the  breakage  of  the  cable,  which  usually  results 
from  a strong  wind  coming  up  suddenly  and  putting  a terrific 
strain  on  the  steel  line  by  jerking  it,  the  observers  are  guided 
in  their  actions  by  the  direction  in  which  the  balloon  moves. 
When  it  is  carrying  them  back  over  their  own  territory,  they  navi- 
gate in  the  same  manner  as  a free  balloon,  coming  to  the  ground 
as  soon  as  a favorable  landing  place  can  be  reached.  Instruction  in 
free  ballooning  is  accordingly  an  important  part  of  the  curriculum 
that  the  kite  balloon  observers  must  go  through.  Should  the 
wind  be  in  the  opposite  direction,  however,  as  only  too  often  proves 
to  be  the  case,  all  instruments,  papers,  and  maps  are  immediately 
thrown  over  the  side  and  the  observers  promptly  follow  suit  in 
their  parachutes,  abandoning  the  balloon  to  its  fate.  As  the 
balloon  travels  with  the  speed  of  the  wind,  once  it  is  released, 
and  the  parachute  of  the  descending  observer  is  carried  in  the  same 
direction,  prompt  action  is  vital  to  prevent  coming  to  the  ground 
in  the  enemy’s  territory.  In  a 30-mile  wind,  for  example,  only 
eight  minutes  would  elapse  from  the  moment  that  the  balloon 
broke  away  until  it  traversed  the  4 miles  intervening  between  its 
station  and  the  enemy’s  lines.  On  some  occasions,  kite  balloons 
which  were  not  fit  for  further  service  have  been  loaded  with 
explosives  and  released  from  a height  that  would  cause  them 
to  land  well  within  the  enemy’s  territory  with  disastrous  results 
to  the  men  detailed  to  capture  them. 

Marine  Service.  The  kite  balloon  was  first  used  by  the 
British  naval  forces  in  their  operations  against  the  Dardanelles  and 


DIRIGIBLE  BALLOONS 


67 


proved  so  valuable  that  they  have  since  been  employed  in  fleet 
expeditions  in  the  North  Sea  as  well  as  for  anti-submarine  work. 
In  the  latter  form  of  service,  they  have  the  same  superiority  over 
the  aeroplane  for  observation  that  they  possess  in  land  operations. 
The  ship  naturally  cannot  run  the  risk  of  remaining  stationary, 
but  as  the  speed  of  the  balloon  is  the  same  as  that  of  the  ship 
towing  it,  the  observers  do  not  pass  over  a given  area,  with  any- 
thing like  the  velocity  of  an  aeroplane,  while  their  elevated  posi- 
tion affords  the  same  advantages  for  detecting  the  presence  of  the 
submerged  submarine  or  the  approach  of  enemy  vessels. 


EXAMINATION  PAPER 


DIRIGIBLE  BALLOONS 


Read  Carefully:  Place  your  name  and  full  address  at  the  head  of  the 

paper.  Any  cheap,  light  paper  like  the  sample  previously  sent  you  may  be 
used.  Do  not  crowd  your  work,  but  arrange  it  neatly  and  legibly.  Do  not 
copy  the  answers  from  the  Instruction  Paper;  use  your  own  words,  so  that  we 
may  be  sure  you  understand  the  subject. 


1.  What  essential  features  of  design  did  Meusnier’s  first 
dirigible  incorporate? 

2.  Describe  the  difference  between  rigid,  semi-rigid,  and 
flexible  types  of  dirigibles. 

3.  State  the  laws  governing  the  increase  of  resistance  with 
speed,  the  increase  of  power  necessary  for  a given  increase  of  speed, 
and  the  ratio  in  which  the  volume  and  area  of  the  gas  bag  increase 
with  increased  dimensions. 

4.  What  provides  the  lifting  power  of  the  dirigible  and  how 
is  this  lifting  power  utilized?  Why  should  this  lifting  power  be  so 
much  less  at  night  than  in  the  daytime?  What  is  net  lifting  power? 

5.  What  are  air  balloonets?  How  and  for  what  purpose  are 
they  used? 

6.  What  is  the  most  efficient  form  of  envelope  for  the  dirigible, 
and  why? 

7.  Why  cannot  the  ordinary  spherical  balloon  be  propelled 
as  a dirigible? 

8.  Is  the  form  of  the  stern  as  important  as  the  bow? 

9.  What  is  longitudinal  stability  and  how  is  it  obtained? 

10.  How  is  stability  of  direction  obtained?  What  are  sta- 
bilizing planes? 

11.  Why  must  a form  of  suspension  for  the  car  that  cannot 
be  accidentally  displaced  with  relation  to  the  balloon  be  provided? 


DIRIGIBLE  BALLOONS 


12.  Theoretically,  where  should  the  propulsive  effort  be  applied 
to  a dirigible?  What  factors  affect  the  placing  of  the  propeller  and 
what  has  been  proved  to  be  the  most  practical  solution  of  the 
problem? 

13.  Discuss  the  advantages  of  the  kite  balloon  over  the  aero- 
plane  for  observation. 

14.  What  is  the  effect  of  the  wind  on  a modern  kite  balloon? 

15.  What  is  the  difference  between  “pounds  per  horsepower” 
and  “pounds  per  horsepower  hour”  as  applied  to  the  motor  of  a 
dirigible?  Which  is  more  important? 

10.  Sketch  and  explain  the  Astra-Torres  suspension. 

17.  What  differences  exist  between  a Zeppelin  and  a Schutte- 
Lanz  dirigible? 

18.  Describe  the  “L-49”,  discussing  power  plant  and  control. 

19.  Define  static  and  dynamic  equilibrium  as  applied  to  the 
dirigible. 

20.  Is  the  Zeppelin  effective?  Discuss  fully. 

After  completing  the  work,  add  and  sign  the  following  statement: 

I hereby  certify  that  the  above  work  is  entirely  my  own. 

(Signed) 


